The antimycotic activity in vitro of jasmon and 6 closely related substances has been tested against four different dermatophytes, Candida albicans, Pityrosporum ovale and Aspergillus fumigatus. Jasmon had the highest activity. Among the other substances tested only thiazolidines with a carbonyl function developed antifungal properties against dermatophytes. 2,4 thiazolidinedione at 450 ppm inhibits the growth of Trichophyton rubrum.