The microbial transformation of iota-menthol (1) was investigated by using 12 isolates of soilborne plant pathogenic fungi, Rhizoctonia solani (AG-1-IA Rs24, Joichi-2, RRG97-1; AG-1-IB TR22, R147, 110.4; AG-1-IC F-1, F-4, P-1; AG-1-ID RCP-1, RCP-3, and RCP-7) as a biocatalyst. Rhizoctonia solani F-1, F-4 and P-1 showed 89.7-99.9% yields of converted product from 1, RCP-1, RCP-3, and RCP-7 26.0-26.9% and the other isolates 0.1-12.0%. In the cases of F-1, F-4 and P-1, substrate 1 was converted to (-)-(1S,3R,4S,6S)-6-hydroxymenthol (2), (-)-(1S,3R,4S)-1-hydroxymenthol (3) and (+)(1S,3R,4R,6S)-6,8-dihydroxymenthol (4), which was a new compound. Substrate I was converted to 2 and/or 3 by RRG97-1, 110.4, RCP-1, RCP-3 and RCP-7. The structures of the metabolic products were elucidated on the basis of their spectral data. In addition, metabolic pathways of the biotransformation of 1 by Rhizoctonia solani are discussed. Finally, from the main component analysis and the differences in the yields of converted product from 1, the 12 isolates of Rhizoctonia solani were divided into three groups based on an analysis of the metabolites. (C) 2003 Society of Chemical Industry.