A series of experiments have been conducted to test the hypothesis that blooms of dinoflagellates ("red tides") may adversely affect year-class strength of northern anchovy, particulary if the red tide occurs during the anchovy spawning season. Experiments were conducted to determine the effects of a variety of dinoflagellate species on the feeding, growth and survival of first-feeding larval anchovy, Engraulis mordax. The dinoflagellate species tested were Gyrodinium dorsum, G. resplendens, Gonyaulax grindleyi, G. polyedra, Protogonyaulax catenella and Gymnodinium splendens. All species occur in southern California waters. Growth experiments were conducted at 16-17ºC using dinoflagellate concentrations > 1,000 mg C liter^-1. Larvae were reared for a period of 9 days. Highest growth rates were obtained on Gymnodinium splendens. Lowest growth rates and survival - no different than on filtered seawater - were obtained on Gonyaulax grindleyi. Survival ranged from almost 90% on Gymnodinium splendens to < 10% on Gonyaulax polyedra and G. grindleyi. Feeding experiments yielded results which are consistent with results of the growth experiments. Fully half the species we investigated appear to have deleterious effects on feeding, growth and survival of larval anchovy. It is concluted that, in years when anchovy are spawned during blooms of Gonyaulax polyedra or Protogonyaulax catenella, poor year-classes may result.