In the present work the occurrence of aflatoxin in peanut (Arachis hypogaea L.) in the region of Monte Alto, S.P., was investigated in three Stages, from harvest to industrialization: a) by the time the grower sells it to the oil mill: Epochs I and II; b) during its storage prior to milling; Epochs III and IV and c) after oil extraction (peanut flour) : Epochs V and VI. In each Stage two collections, of 10 samples each, were made in a total of 40 samples of peanuts and 20 samples of peanut flour. From the results the following conclusions could be drawn: 1) the majory of the samples, representing 90%, was toxic; 2) the toxicity level, in terms of aflatoxin B1,was hight for 60% of the samples had more than 1.00 ppm, in the category "Very Hight" ; 3) the toxicity level of the samples grew from Epoch I to Epoch IV: mean values of 0.10 to 2.49 ppm, decreasing in Epochs V and VI: 1.02 and 1.25 ppm, giving the average value of 1.23 ppm; 4) aflatoxin is already present in peanuts when the grower take it to the oil mill; 5) storage at the oil mill seems to contribute to increase the toxicy level.