The strategy of training community health extension workers in rural Nigeria to promote exclusive breast feeding was evaluated in a survey of 66 trained primary health care workers in the Ife South Breast Feeding Project area and 56 primary health care workers in seven non-intervention districts. Although breast feeding is widespread in Ife South, understanding of the importance of early initiation of breast feeding, use of colostrum, and prolonged exclusive breast feeding was deficient. Focus group discussions before the training revealed no differences in the breast feeding knowledge of health workers from the intervention and control areas. A workshop for trainers in the study area was followed by district-level workshops led by these trainers. Initiation of breast feeding within 30 minutes of delivery was reported for 32% of deliveries in the intervention area compared with only 6% in the control group. Trained workers had better knowledge of and attitudes toward breast feeding than controls and were significantly more likely to recommend exclusive breast feeding for 4-6 months. Multivariate analysis of breast feeding knowledge scores showed that location in the study area and participation in training were the only variables that contributed significantly to improve overall scores. In rural Nigeria, where over 75% of mothers have contact with primary health care workers, incorporation of breast feeding training into the primary health care system is recommended.