The action of Trichomycin on the respiration and phosphorus metabolism of Trichophyton gypseum was examined. This antibiotic stimulated the respiratory rate of this fungus in a range of 0.1∼100γ/cc., while it inhibited the rate markedly over 100γ/cc. The inhibitory action of Trichomycin upon the incorporation of phosphate into the cells from the surrounding medium was demonstrated with the aid of 32P-labeled phosphate. Such an effect appeared from 0.1γ/cc.