The storage disaccharide, trehalose, is accumulated in yeast during a temperature shift from 30 to 45 degrees C. The response peaks at 90 min and is transient since levels of trehalose decline rapidly in cells returned to 30 degrees C. Storage of trehalose is inhibited when cells are incubated in the presence of acridine orange or ethidium bromide prior to and during temperature shift, suggesting a requirement for de novo RNA synthesis. Accumulation of trehalose occurs when cells are exposed to either ethanol, copper sulphate or hydrogen peroxide at 30 degrees C, indicating that the phenomenon may be a general response to physiological stress. Parallels are drawn between the trehalose accumulation response and the heat shock response in yeast.