Several tester strains of Salmonella typhimurium, TA-98, TA-100, TA-1535, and TA-1538; Escherichia coli, W3110 (pol A+) and p3438 (pol A-, repair deficient); and Saccharomyces cerevisiae, D3, D4, and D5 were tested for lethal and mutagenic events when exposed to elevated temperatures or to x-band, pulsed microwave radiation at various power densities. When compared to E. coli pol A+ under growing conditions, E. coli pol A- exhibited decreased cell growth when exposed to microwave radiation at power levels at or above 20 mW/sq. cm. as well as to temperature levels above 42 C. All yeast and other bacterial strains showed cellular lethality at similar microwave intensities and elevated temperatures. When exposed to elevated temperatures in saline, both quiescent yeast and Salmonella strains exhibited lethal events.