The whole proteins from 10 different Saccharomyces species were separated by isoelectric focusing, which was carried out in pH gradient polyacrylamide gels with the carrier ampholytes of various pH ranges. About 25 protein bands were found in the gel using pH 3.0-10.0 carrier ampholytes. In gel using pH 4.0-7.0 carrier ampholytes, the protein band of pI 6.3 was found in Sacch. cerevisiae NCYC 478, ATCC 26787, Sacch. rosei and Sacch. uvarum, but it was absent in Sacch. cerevisiae ATCC 24903, ATCC 42949, ATCC 36029, Sacch. steineri var hara, Sacch. bayanus, and Sacch. diastaticus.