Musashi has been identified as an RNA-binding protein thought to be involved in asymmetric divisions during Drosophila neural development. To analyze expression patterns of mammalian Musashi homolog Musashi-1 in human normal colon crypt, 155 colon crypts separated from biopsy specimens of normal colonic mucosa were evaluated. Specimens were fixed, microdissected to isolate a few crypts, immunostained with anti-Musashi-1 antibody (14H1), and examined under confocal laser scan microscopy. The number of Musashi-1-positive cells in each crypt was 19.0 +/- 7.53 (mean +/- SD). Most Musashi-1 positive cells were located at the crypt base, between cell positions 1 and 10. Distribution of Musashi-1-positive cells corresponded with that of stem cells, as outlined in previous reports, implying that Musashi-1 is a key control element of asymmetrical division within the colon crypt. This is the first report outlining expression of Musashi-1 in human colon crypt cells.