Cells of a heat-shock resistant mutant were approximately 1000-times more resistant to lethal heat shock than those of the parental strain. We observed that exponentially growing cells of the mutant synthesized trehalose and showed increased osmotolerance, dehydration tolerance an ethanol tolerance, a fact not observed in wild type strains. The mutant synthesizes constitutively six proteins, among them two proteins of 56 and 63 kDa. Interestingly these molecular weights could correspond to the subunit of trehalose-6-phosphate synthase and to phosphoglucomutase II, respectively. Our results showed that glucose-growing cells of the hsr 1 mutant possessed high levels of activity of these enzymes when compared to the control strain.