Crassostrea gigas larvae were collected in the bay of Arcachon in July 1985, 1986 and 1987. Larval samples were collected daily at high tide, during at least the first 12 days of pelagic life and every hour during 1 day and night cycle, 6 days after spawning. Epifluorescence microscopy was used for detecting ingestion and digestion of nanoplankton and thin sections were made to try to determine the algal species ingested. The first algal uptake occurred 48 hours after fertilization. and different stages or digestion were noted from the 3rd day. No relationship between ingestion or digestion and the age of the veligers was observed. There was no difference in the feeding activity during day and night. Because the nutrition index was high (70%) the feeding behaviour of the larvae was apparently normal. Nevertheless the intensity of algal uptake was weak. The presence of diatoms in the digestive tract suggests that the Bacillariophyceae play a significant role in the nutrition of veligers in nature.