The application of heat shock to different types of cells is known to cause multiple biochemical and metabolic changes. The predominant event though is an increased synthesis and expression of a family of proteins, the heat-shock proteins (Hsp). Some of these proteins are currently considered to be involved in the signal transduction pathway. We investigated for any possible effects of heating fresh normal peripheral T-cells and T-cell lines, on the early signal transduction events which follow the antigen (Ag) receptor-complex (TCR/CD3) crosslinking. More specifically, the Ag-receptor-initiated free cytoplasmic Ca2+ ([Ca2+]i) responses and the production of inositol 1,4,5-trisphosphate (IP3) were evaluated. Heating fresh unmanipulated peripheral T-cells 8 hours before the TCR/CD3 stimulation resulted in decreased [Ca2+]i responses. This was also true for cells of normal short-term T-cell lines as well. The TCR/CD3-mediated production of IP3, which is a mediator of the [Ca2+]i response, was also decreased in heat-shocked T-cells.