The natural occurrence of aflatoxin B1 (AFB1) and sterigmatocystin (ST) has been surveyed in 30 samples of commerical green and roasted coffee. AFB, and ST were found in one out of ten green coffee samples at levels of 25 and 64 ug/kg, respectively. No toxin was found in 20 samples of light and dark roasted coffee. The effect of caffeine on the growth and toxigenic potential of A. parasiticus and A. nidulans was examined in normal and decaffeinated coffee, as well as, in YES medium supplemented with different caffeine concentrations. Caffeine exhibit minor or no effect on fungal growth, but totally prevented the formation of AFB1 and ST in normal coffee. Decaffeinated green coffee induced the production of AFB1 and ST, but this stimulatory effect was decreased with roasted samples. Production of AFB1 and ST in caffeinated YES medium was depend on caffeine concentration and incubation time. AFB1 commenced to arise in small quantity after 21 days of incubation in the presence of 0.6% caffeine. Meanwhile, ST production decreased and delayed up to 14 days of incubation at 0.3% caffeine And completely inhibited at 0.6% caffeine. Data of this study help explain why coffee and other caffeine- containing commodities are poor substrates for mycotoxin production