Aflatoxin production by Aspergillus parasiticus NRRL 2999 was inhibited when Ca2+ channel blockers, i.e., verapamil and diltiazem (> 1 mmol 1(-1)), were included in the culture medium. Inhibition was not accompanied by growth inhibition, nor was the [14C]-glucose uptake by the organism altered. However, both the compounds inhibited [14C]-acetate incorporation into aflatoxin B1 in a dose-dependent manner and decreased sporulation of the organism. Even though a nutritional role for Ca2+ has not been demonstrated unequivocally in fungi, the present study suggests the importance of Ca2+ in the production of these secondary metabolites.