Using 3 species of fungi, the fungistatic and fungicidal actions of clavacin were investigated. The presence of 0.02%, and with some samples 0.01%, of clavacin in the culture medium completely inhibited the growth of Trichophyton gypseum. A concentration of 0.001% of clavacin caused partial inhibition while 0.0001% caused no detectable effect. In contrast, the presence of 0.04% of clavacin had but a slight inhibitory effect on Monilia albicans and Oidium asteroides.