A preliminary field study was conducted on red-bellied lemurs (Lemur rubriventer) in a southeastern rainforest of Madagascar during June and July 1986. Data were collected on diet, patterns of activity, and group composition. In June, the major food resource exploited by L. rubriventer was fruit. The study group also maintained a strict diurnal activity cycle. In July, L. rubriventer fed on flowers (80%), fruits (10%), and leaves (10%) and were nocturnal as well as diurnal. Eucalyptus flowers were the only resource exploited during feeding sessions. L. rubriventer's transition from a diurnal to a random, 24-hour or “cathemeral” activity pattern may be a potential adaptive strategy to avoid predation by diurnal raptors.