The Microbial Identification System (Microbial ID, Inc., Newark, DE), used to identify and characterize fatty acids of bacteria, was modified to characterize fatty acids of isolates of Rhizoctonia solani AG-1 IA. The major fatty acid found was linoleic (18:2 cis 9, 12), which constituted 75.3 - 78.5% of the whole-cell fatty acid content. This fatty acid, along with palmitic (16:0) and oleic (18:1 cis 9), accounted for 95-96% of the C9-C20 fatty acids present. Smaller amounts of nine other fatty acids were consistently identified.