Yeast cells accumulate the disaccharide trehalose in response to certain stress conditions. In an attempt to verify the role that trehalose plays when yeast cells are faced with heat stress, yeast mutant strains with specific lesions in trehalose metabolism were used. Cultures growing exponentially on glucose were shifted from 28 to 40 degrees C for 1 h. Accumulation of trehalose was correlated with heat tolerance, measured as resistance to 50.5 degrees C. Additionally, it was observed that the trehalose carrier was not involved in the mechanism of thermotolerance acquisition. Mutants that lack the carrier were also able to acquire thermotolerance as long as synthesis of the disaccharide took place.