The possible existence of thermal effects specific to microwaves at 2.45 GHz and not found with classical heating in a waterbath was studied by measuring cell survival (colony-forming ability) and cell viability (the ability to exclude trypan blue) in Chinese hamster V79 cells. The microwaves were employed at high power densities (125 to 175 mW/cm2) corresponding to specific absorption rates ranging between 62 and 87 mW/g. When matching the rises in temperature, the effects of microwave-induced hyperthermia at 125 mW/cm2 on cell survival were comparable to those of classical heating. However, they were statistically significantly different when using power densities of 150 and 175 mW/cm2. The response obtained in terms of cell viability appeared to be comparable. The conclusions are also valid when taking into account a correction factor for energy losses during microwave treatment. The apparent specific effect of microwaves appears to be associated with exposures at high power densities involving short treatment times and rapid rises in temperature.