To identify cultural beliefs and practices to evaluate the acceptability of dietary supplements of Oportunidades Program. Ethnographic study with in-depth interviews (n=43)--mothers of children less than five years of age and pregnant and breasfeeding women (PBW)--, key informants (n=9); focus groups (n=8) and direct observation, in four communities from North, Central, South and Southwest of Mexico. The supplement was prepared in several different ways. The liquid preparation was best accepted; generally the supplement was mixed with milk. Initially, the supplement caused nausea, vomiting and diarrhea, but these symptoms disappeared with continued consumption. Acceptance was highest among PBW. The supplement tends to replace milk as a food product in the daily diet. There is a necessity to develop culturally specific evaluations in regions with different food intake practices. The study results should be interpreted in the context of other program components, such as health care and education.