In July 1990, an observer program was established to collect data on the bycatch of the drift and set gillnet fisheries operating off the coast of California. These data are used for estimating mortality and for further studies of the biology of the species impacted. To date, 16 species of Cetacea have been identified in the observed incidental kill of the gillnet fisheries. In the drift gillnet fishery, observers reported 348 cetaceans incidentally killed, and biological samples were collected from 83.6% of these animals. The common dolphin, Delphinus delphis, was the most frequently observed species entangled in the drift gillnet fishing gear and comprised 48.6% of the observed incidental kill. In the set gillnet fishery, 20 cetaceans were observed killed. and biological samples were collected from five of these animals. The harbour porpoise, Phocoena phocoena, was the most frequently observed species entangled in set gillnet gear and comprised 80% of the observed incidental kill. In this report, we summarise, by species, the age, the total body length and the sex composition of cetaceans sampled from the incidental kill in the drift gillnet fishery between July 1990 and December 1995, and in the set gillnet fishery between July 1990 and Decemher 1994. We also demonstrate the value of collecting small samples of skin tissue for confirming species identification using molecular genetic techniques.