A primary cellular site involved in heat shock response of eukaryotic cells is located in plasma membranes. The mechanism by which heat shock is sensed and the signals that trigger heat shock response remain an enigma. We aim to determine the role of guanine-nucleotide binding proteins (G)-proteins in mediating heat shock response in eukaryotic cells. The effect of heat shock on high affinity GTPase activity in presence or absence of modulators of G-proteins, such as pertussis toxin was studied by measuring GTPase catalyzed release of 32[P i] from γ- 32[P]GTP. The effect of pertussis toxin on induction of heat shock proteins in cells subjected to thermal stress was studied by SDS-PAGE analysis of 35[S]-methionine labelled cellular proteins. Exposure of cultured human malignant cells to thermal stress (43°C) resulted in a significant increase in activity of high affinity GTPase in the membranes ( P < 0.001). This response to heat shock was inhibited by prior exposure of the cells to nanogram concentrations of pertussis toxin, suggesting the involvement of G-proteins in mediating heat shock response. To characterize this G-protein dependence further, we assayed thermal stress stimulated high affinity GTPase activity in cells pretreated with antisera (AS/7) raised against a synthetic peptide corresponding to the last 10 amino acids of α-subunit of inhibitory G-protein (G i). A partial reduction in heat shock induced stimulation of GTPase activity was observed in the presence of this antisera. The pertussis toxin treated cells did not show induction of heat shock proteins in response to thermal stress. The inhibition of heat shock induced stimulation of high affinity GTPase by pretreatment of cells with pertussis toxin or antiserum against G i and inhibition of induction of heat shock proteins in toxin treated heat shocked cells suggests that G-protein(s) play a role in mediating the heat shock response.