The anthelmintic agent methyl 5(6)-butyl-2-benzimidazolecarbamate (Parbendazole) was transformed to two of its animal metabolites, methyl 5(6)-(4-hydroxybutyl)-2-benzimidazolecarbamate and methyl 5(6)-3-(carboxypropyl)-2-benzimidazolecarbamate, by the filamentous fungus Cunninghamella bainieri ATCC 9244. The transformation pathway was shown to be through the 4-hydroxybutyl product to the 3-carboxypropyl product. The reaction favored accumulation of the latter product.