In the studies on the 18S and 26S rRNA partial base sequencings (one region in 18S rRNA and two regions in 26S rRNA) over the past six years, the following conclusions were obtained. 1) In the partial base sequencings of 18S rRNA (position 1451-1618, 168 bases), the separate genus or genera can be set up, when the calculated number of base differences was five or more. 2) Generally, the base substitutions occurred more frequently in the 26S rRNA (positions 1611-1835, 225 bases and positions 493-622, 130 bases) than those in the 18S rRNA (position 1451-1618, 168 bases). Between Nematospora coryli (Q-5 or Q-6) and Holleya sinecauda [Q-9 (Q-8)], however, the base differences were large and numbered seven in the partial base sequencings of 18S rRNA (positions 1451-1618, 168 bases) but only two in those of 26S rRNA (positions 1600-1835, 236 bases). 3) The genus Williopsis Zender, delimited by Kurtzman, was divided into three groups or more (Zygowilliopsis and Komagataea). 4) The nitrate-assimilating Pichia species, which were once classified in the genus Hansenula Sydow et Sydow, were divided into seven groups, and Ogataea, Kuraishia and Nakazawaea were proposed. 5) Of the methanol-assimilating yeasts, Pichia pastoris was phylogenetically distant and Komagataella was proposed. 6) Several problems in the partial base sequencings were presented and discussed phylogenetically and taxonomically.