Sporidesmin, a mycotoxin produced by some strains ofPithomyces chartarum, is responsible for the hepatogenous photosensitisation disease facial eczema, which causes severe losses in agricultural revenue in New Zealand. A sporidesmin-producing strain ofP. chartarum, isolated in New Zealand, was grown in co-culture with a South African strain that does not produce the mycotoxin. Competition occurred between the two strains when grown both on agar plates and on dried ryegrass, with a significant decrease in the total amount of sporidesmin produced. Biological control of toxkenicP. chartarumcan thus occur under laboratory conditions, raising the possibility of similar control in the field situation.