Cellular expression of the 72 kD heat shock protein (72 kD hsp) is increased following exposure to a wide range of physical and chemical stimuli and may be useful as a marker of cell toxicity. The primary objective of this work was to develop a cytochemical method suitable for the detection and cellular localization of stress-inducible 72 kD hsp mRNA and protein in cell cultures. Swiss 3T3 mouse fibroblasts, grown on multi-chamber glass slides, were transiently exposed to an elevated incubation temperature or various chemical agents and cellular 72 kD hsp expression visualized using immunocytochemical and in situ hybridization detection methods. Expression of 72 kD hsp was found to be dependent on the applied stimulus and recovery time. The combined culture system and cytochemical assay for 72 kD hsp provides a convenient method for studying cellular responses to a variety of toxins.