Under favorable growth conditions, Aspergillus flavus and A. parasiticus produced aflatoxins on marihuana. Cultures of A. flavus ATCC 15548 produced both aflatoxin B1 (AFB1) and G1 (AFG1). The production of AFG1 was substantially greater than that of AFB1. Cultures of A. flavus NRRL 3251 and A. parasiticus NRRL 2999 produced only AFB1. All natural flora cultures tested negative for aflatoxins. No Aspergilli sporulations were observed in these cultures. In the cultures inoculated with known toxigenic fungi, the highest mean level for total aflatoxins was 8.7 microgram/g of medium. Marihuana appears not to yield large quantities of these mycotoxins but sufficient levels are present to be a potential health hazard for both the user and the forensic analyst who is in daily contact with such plant material. Careful processing, storage, and sanitation procedures should be maintained with marihuana. If these conditions are disregarded due to the illicit status of marihuana, the potential for mycotoxin contamination must be considered.