This study was performed to determine the cytogenetic effects of short-term thermal stress in human cultured lymphocytes. Experimental heat shock (39 degrees C) was performed alone or with the addition of mitomycin C (MMC) to determine the synergistic or antagonistic effects of heat shock on genotoxicity induced by MMC. In this study, during culture periods of 72 h, human peripheral blood lymphocytes were exposed to heat shock for specified durations (30, 60, 120, and 240 min) 24 or 48 h before harvest. According to our results, the selected temperatures did not show genotoxic or mutagenic effects. In summary, the heat shock tested did not show any cytogenetic effect on the cultured blood cells and did not cause significant alterations in genotoxicity induced by MMC.