SummaryGastrodia elata was collected from July to August 1992 in Hokkaido forests. A total of 22 diploid isolates were paired with haploid testers of the biologicalArmillariaspecies reported in Hokkaido. One isolate was identified asA. ostoyae, 10 asA. gallica, three asA. jezoensis, three asA. sinapina, and five asA. singula. These isolates were compatible with the respective Hokkaido testers of these species. With the exception of A. ostoyae, these species are known as saprophytes, which form abundant rhizomorphs in soil.Clear isozyme profiles of esterases were obtained with all isolates except one. Interspecific variations were more important than intraspecific variations. The esterase profiles could be used for identification of theArmillariaspecies in Hokkaido as a useful complement to the mating‐type metho