The acute reactions of skin of the thigh-leg of normal young adult C3Hf/Sed mice following five equal radiation doses (60Co) were studied in mice irradiated at various leg skin temperatures and while respiring various gas mixtures in control or anesthetized condition (sodium pentobarbital, 0.05 mg/g-1 body wt.) At 25 and 35 degrees C, anesthesia reduced the RD50 (2.5+ reaction) by 4-5%. An increase of temperature from 25 to 35 degrees C resulted in a decrease in RD50 by 10-12% for subjects respiring air or 5% for subjects respiring O2 at 1 or at 3 ATA. The major modifier of radiation response was to change from respiration of air to O2 at 1 or 3 ATA. Enhancement ratios for RD50 Air/O2 1 ATA were 1.4-1.5 for 25 and 35 degrees C. The ratios O2 1 ATA/3 ATA were 1-1.05.