Dermatophytes are usually isolated from house dust by using actidione-chloramphenicol Sabouraud glucose medium (ACS medium). We have prepared a new medium, 5FC medium, by adding gentamicin sulphate (GS) and 5-fluorocytosine (5FC) to ACS medium to achieve more efficient isolation of dermatophytes from house dust. 5FC medium was more effective in isolating dermatophytes than ACS medium or ACS medium supplemented with GS alone. Trichophyton rubrum could be grown from 13 out of 19 house dust samples from the homes of patients with tinea pedis (68.4%), and T. mentagrophytes could be grown from 17 out of 21 (81.0%). Two of 20 house dust samples from the home of a control family without dermatophytosis grew only one colony of dermatophytes in 5FC medium; the rest of the samples showed no growth. The number of colonies isolated on 5FC medium was much higher than on ACS medium (5.3 vs. 2.0 for T. rubrum and 17.2 vs. 2.1 for T. mentagrophytes). In addition, the size of the isolated colonies was much larger than that on ACS medium. Thus, 5FC medium can be regarded as a useful tool for isolating dermatophytes from various contaminated samples.