The fumonisin B 1 (FB₁) contamination of maize collected in two areas of Iran during 1999 was determined. The 20 maize samples from Mazandaran Province, situated on the Caspian littoral of Iran, consisted of random samples of farmers' lots and were all contaminated with FB₁ at a mean level of 3.18 mg kg^-1 (range 0.68-7.66 mg kg^-1). The 10 samples (of the same maize cultivar) from Isfahan Province in central Iran were purchased as maize cobs in local retail markets and had mean FB levels of 0.22 mg kg^-1 (mean of all samples, 6/10 samples positive, range <0.01-0.88 mg kg^-1). The FB levels in Mazandaran, an area of high oesophageal cancer, were significantly (p < 0.0001) higher than the FB₁ levels found in maize from Isfahan, an area of low oesophageal cancer in Iran.