Many of the changes induced in yeast by sublethal yet stressful amounts of ethanol are the same as those resulting from sublethal heat stress. They include an inhibition of fermentation, increased induction of petites and stimulation of plasma membrane ATPase activity. Ethanol, at concentrations (&lo%, v/v) that affect growth and fermentation rates, is also a potent inducer of heat-shock proteins including those members of the Hsp7O protein family induced by heat shock. This induction occurs above a threshold level of about 4% ethanol, although different heat-shock proteins and heat-shock gene promoters are optimally induced at different higher ethanol levels. In addition ethanol ( 6 8 % ) causes the same two major changes to integral plasmamembrane protein composition that result from a sublethal heat stress, reduction in levels of the plasma membrane ATPase protein and acquisition of the plasma membrane heat-shock protein Hsp30.