A need was identified for an in vitro system that would correctly identify testicular toxicants. This model would have present all the cell types found in the testis, and would be capable of metabolizing xenobiotics to active or inactive metabolites. Initial efforts are aimed at generating a reproducible culture, and characterizing the populations of cells therein. Specific secretory products have been identified as markers of cell function, and assays for these are being set up and validated.