In the present study, the risk of exposure to aflatoxin in infants fed breast milk and formula was investigated. For this purpose, aflatoxin B-1 (AFB(1)) was determined in the serum of both breast-fed and formula-fed infants. Serum AFB(1) positivity was significantly higher in the formula-feeding (F) group than the breast-feeding (B) group (42.8 vs 8.5%, P < 0.01). The AFB(1) concentration in different commercial formulas was also determined. Aflatoxin B-1 was found in seven of the eight newly opened packages of different brands of formula. The concentrations showed a statistically significant increase at the 30th day after opening the packages (P < 0.01). Although AFB(1) concentrations in the formulas were found to be within acceptable limits for most countries, still, its existence must be carefully evaluated because future influences of very small amounts of aflatoxin on the growing organism have not been fully elucidated. Therefore, it was again concluded that for infants, human milk is safer than commercial formulas because of the lower contamination risk of aflatoxin. Also, commercial formulas must be regularly examined by authorities for the possible risk of aflatoxin contamination.