diff --git a/README.md b/README.md
index 6bbc774..e847415 100644
--- a/README.md
+++ b/README.md
@@ -132,6 +132,8 @@ options:
   -t, --threads THREADS
                         number of alignment threads. A sensible default is chosen automatically
                         (default: 10)
+  --output-bam          save mapped reads to BAM for downstream analysis
+                        (default: False)
   --force               overwrite existing output files
                         (default: False)
   --airplane            disable automatic index download (offline mode)
diff --git a/src/hostile/aligner.py b/src/hostile/aligner.py
index 439d89c..b7a3efc 100644
--- a/src/hostile/aligner.py
+++ b/src/hostile/aligner.py
@@ -139,6 +139,7 @@ def gen_clean_cmd(
         aligner_threads: int,
         compression_threads: int,
         force: bool,
+        output_bam: bool,
     ) -> str:
         fastq, output = Path(fastq), Path(output)
         output.mkdir(exist_ok=True, parents=True)
@@ -146,6 +147,13 @@ def gen_clean_cmd(
         fastq_out_path = output / f"{fastq_stem}.clean.fastq.gz"
         count_before_path = output / f"{fastq_stem}.reads_in.txt"
         count_after_path = output / f"{fastq_stem}.reads_out.txt"
+        mapped_bam_path = output / f"{fastq_stem}.mapped.bam"
+
+        bam_cmd = (
+            f" | tee >(samtools view -F 2304 -b - > '{mapped_bam_path}')"
+            if output_bam
+            else ""
+        )
 
         if not stdout and not force and fastq_out_path.exists():
             raise FileExistsError(
@@ -196,6 +204,8 @@ def gen_clean_cmd(
         cmd = (
             # Align, stream reads to stdout in SAM format
             f"{alignment_cmd}"
+            # optional - output bam
+            f"{bam_cmd}" 
             # Count reads in stream before filtering (2048 + 256 = 2304)
             f" | tee >(samtools view -F 2304 -c - > '{count_before_path}')"
             # Discard mapped reads (or inverse)
@@ -228,6 +238,7 @@ def gen_paired_clean_cmd(
         aligner_threads: int,
         compression_threads: int,
         force: bool,
+        output_bam: bool,
     ) -> str:
         fastq1, fastq2, output = Path(fastq1), Path(fastq2), Path(output)
         output.mkdir(exist_ok=True, parents=True)
@@ -237,6 +248,13 @@ def gen_paired_clean_cmd(
         fastq2_out_path = output / f"{fastq2_stem}.clean_2.fastq.gz"
         count_before_path = output / f"{fastq1_stem}.reads_in.txt"
         count_after_path = output / f"{fastq1_stem}.reads_out.txt"
+        mapped_bam_path = output / f"{fastq1_stem.removesuffix('_R1_paired')}.mapped.bam"
+
+        bam_cmd = (
+            f" | tee >(samtools view -F 2304 -b - > '{mapped_bam_path}')"
+            if output_bam
+            else ""
+        )
 
         if (
             not stdout
@@ -320,6 +338,8 @@ def gen_paired_clean_cmd(
             )
         cmd = (
             f"{alignment_cmd}"
+            # optional - output bam
+            f"{bam_cmd}" 
             f" | tee >(samtools view -F 2304 -c - > '{count_before_path}')"
             f"{filter_cmd}"
             f" | tee >(samtools view -F 2304 -c - > '{count_after_path}')"
diff --git a/src/hostile/cli.py b/src/hostile/cli.py
index 6cf3079..a50d6cc 100644
--- a/src/hostile/cli.py
+++ b/src/hostile/cli.py
@@ -34,6 +34,7 @@ def clean(
     force: bool = False,
     airplane: bool = False,
     debug: bool = False,
+    output_bam: bool = False,
 ) -> None:
     """
     Remove reads aligning to an index from fastq[.gz] input files or stdin.
@@ -53,6 +54,7 @@ def clean(
     :arg force: overwrite existing output files
     :arg airplane: disable automatic index download (offline mode)
     :arg debug: show debug messages
+    :arg output_bam: save mapped reads to BAM for downstream analysis
     """
 
     if debug:
@@ -81,6 +83,7 @@ def clean(
             threads=threads,
             force=force,
             airplane=airplane,
+            output_bam=output_bam,
         )
     else:
         stats = lib.clean_fastqs(
@@ -96,6 +99,7 @@ def clean(
             threads=threads,
             force=force,
             airplane=airplane,
+            output_bam=output_bam,
         )
     print(
         json.dumps(stats, indent=4),
diff --git a/src/hostile/lib.py b/src/hostile/lib.py
index 20052b8..8ecd3ce 100644
--- a/src/hostile/lib.py
+++ b/src/hostile/lib.py
@@ -174,6 +174,7 @@ def clean_fastqs(
     threads: int = util.CPU_COUNT,
     force: bool = False,
     airplane: bool = False,
+    output_bam: bool = False,
 ):
     stdin = str(fastqs[0]) == "-"
     stdout = str(output) == "-"
@@ -212,6 +213,7 @@ def clean_fastqs(
             aligner_threads=aligner_threads,
             compression_threads=compression_threads,
             force=force,
+            output_bam=output_bam, 
         )
         for fastq in fastqs
     ]
@@ -252,6 +254,7 @@ def clean_paired_fastqs(
     threads: int = util.CPU_COUNT,
     force: bool = False,
     airplane: bool = False,
+    output_bam: bool = False,
 ):
     stdin = str(fastqs[0][0]) == "-"
     stdout = str(output) == "-"
@@ -292,6 +295,7 @@ def clean_paired_fastqs(
             aligner_threads=aligner_threads,
             compression_threads=compression_threads,
             force=force,
+            output_bam=output_bam, 
         )
         for fastq_pair in fastqs
     ]