Temperature-sensitive (ts) mutants of Saccharomyces cerevisiae Y-196 were isolated by using UV irradiation and/or EMS treatment. They grew normally at permissive temperature (30 degrees C), but could not grow at restrictive temperature (38 degrees C). From chemical composition analysis, it was found that ts mutants AMY-159, and AMY-88 had the highest protein and RNA contents, respectively. When the cells were cultivated at 30 degrees C to stationary phase and then shifted to 38 degrees C for 4 hr, protein contents of wild-type and most of the ts mutants increased but RNA contents decreased. Glutamic acid, aspartic acid and lysine were the three major amino acids of protein in all isolates tested at both temperatures. When the ts mutants AMY-136, AMY-161, and AMY-157 were cultured at 38 degrees C for 4 hr, methionine contents increased Amino acid scores of ts mutants AMY-15 and AMY-88 increased when they were shifted to 38 degrees C for 2 to 4 doubling times. The amounts of amino acids produced in some ts mutants were higher than that of wild-type.