Effect of treatment with different doses of citreoviridin, a mycotoxin from Penicillium citreoviride NRRL 2579, inhibited the brain GAD activity both under in vivo and in vitro conditions with concomitant reduction in GABA level. GABA-T activity is unaltered except in vitro in cerebral hemispheres where an increase is noted. It is suggested that citreoviridin neurotoxicity is related to the GABA metabolism of central nervous system. © 1983.