Assay for telomerase on cultures of a variety of dogfish shark and little skate cell types showed that all cultures tested were positive, although specific activity varied almost 100-fold among different cell types. Assay for cell proliferation by in situ bromo-deoxyuridine (BrdU) incorporation also was carried out on cultures from shark brain, kidney and rectal gland. The assay involves an overnight incubation with BrdU, followed by an immunoassay identifying cells synthesizing DNA during the time of incubation and incorporating the nucleoside analogue. The results showed that cells in the cultures were synthesizing DNA. The most active synthesis was seen in cultures from early shark embryos. Medium was supplemented with insulin, tranferrin, selenous acid, EGF, FGF, Lglutamine, chemically defined lipids, non-essential amino acids, heat-inactivated fetal bovine serum (heat treated for 30 min at 56°C) and shark yolk extract. Conditioned medium from the cells was stimulatory for other shark cell cultures, including the shark rectal gland cells ( Figure 5) . A normalized c-DNA library has been made from these cells and attempts will be made to identify the cell type by extensive EST analysis.