Aflatoxin M1 was surveyed in 300 samples of whole milk powder consumed by infants at municipal schools and nurseries in São Paulo, Brazil. The analyses were performed by using commercially available test systems of a direct competitive enzyme-linked immunosorbent assay (ELISA). Samples were reconstituted in water (1:8), centrifuged at 1630 x gav for 15 min, and submitted directly to the assay without clean-up procedures. Results showed 33 (11%) positive samples for aflatoxin M1 at levels of 0.10-1.00 ng/ml (mean: 0.27 +/- 0.20 ng/ml). By using data on milk consumption patterns for 4-month-old children (highest intake), a mean daily intake of 3.7 ng/kg body weight/day was estimated. The implications of these data on human health are discussed.