The fatty acids ofTrichophyton rubrum found during the logarithmic growth phase and during the early and late stationary phases of growth were separated and identified by gas chromatography. At all three stages of growth, the most abundant fatty acids were palmitic, stearic, octadecenoic and octadecadienoic which, together, accounted for 85–93% of the total fatty acid content. With age, there appears to be a tendency toward chain elongation and desaturation. Analysis of the fatty acid content of a pigmented culture indicated the presence of 8 unsaturated fatty acids which accounted for 65% of the total fatty acids isolated, octadecadienoic acid alone contributing almost 50% to this figure.