Benzamide, an inhibitor of poly (ADP-ribose) synthetase, which augments chondrocytic differentiation, significantly decreased poly (ADP-ribose) synthetase activity in cultured chick limb bud cells. Benzamide significantly increased cell proliferation, but did not affect DNA synthesis per cultured cell. Furthermore, benzamide significantly increased NAD levels and synthesis, while it did not affect ATP levels and synthesis except for ATP synthesis on day 1. Thus, we suggest that benzamide augments both cell proliferation and NAD synthesis during chondrocytic differentiation.