Introduction: Aflatoxins, known as causative factors of hepatic and extra-hepatic carcinogenesis within humans, are extremely teratogenic, mutagenic, toxic, and carcinogenic compounds.

Materials & Methods: This study was undertaken to determine the occurrence of aflatoxin M₁ (AFM₁) in 40 raw milk and 47 pasteurized milk samples collected during spring and winter. In order to analyze the samples, the Enzyme-linked Immunosorbent Assay (ELISA) procedure was used. The statistical methods used in this study were based on normal confidence intervals and analysis of variance (ANOVA).

Results: Aflatoxin M₁ was detected in 97.5% of the raw milk ranging from 6.52 to 68.17 ng/l and 95.7% of the pasteurized milk, ranging from 0.8 to 58.13 ng/l. Toxin levels in 10% of the raw milk and 2.1% of the pasteurized milk samples exceeded the Iranian national standard limit i.e. 50 ng/l.  Due to seasonal variations, mean concentration of AFM₁ in the samples collected in winter was significantly (P < 0.03) higher than those collected in the summer.

Conclusion: Large amount of AFM₁ in milk samples might be a potential hazard for the public health. Reducing the levels of AFB₁ in animal feedstuffs can be regarded as the initial step to control the transfer of AFM₁ to humans.