A strain of T. mentagrophytes, typically sensitive to C6-C12 fatty acids, was grown with constant aeration at pH 6.5 and found to contain (dry weight basis) 15.2% lipid. The glyceride fraction contained 95% fatty acids; the nonsaponafiable portion consisted of a mixture of unidentified sterols. The total unfractionated lipid had antifungal activity against the host organism at pH 6.0, suggesting the presence of unesterified long chain fatty acids. A strain of Aspergillus niger, comparatively resistant to fatty acids, was similarly grown and found to contain 17.5% lipid. It was concluded that susceptibility to lipophilic agents such as the fatty acids is not related to total lipid content.