This study investigated the effects of local preoperative radiation on the tissue resistance to surgical infection. Preoperative radiation was given to the skin of the backs of 144 rats in two doses and wounded at intervals after the radiation. As determined by quantitative bacterial counts of the wounds 4 days after wounding, 80 to 100 percent of the rats in each group healed their wounds with counts that were 10(3) organisms per gram, or less, in spite of the dose of radiation or the interval to wounding. In an additional 560 rats, 10(4) S. aureus organisms were inoculated into the surgical wounds made at various intervals after three doses of radiation. In this part of the study, the rates of infection (as determined by bacterial counts of 10(5) per gram or more) increased significantly with the increasing dose of radiation, as well as with the increasing interval from radiation to wounding. These data demonstrate that radiated tissue cannot tolerate bacterial contamination as well as normal tissue. Since surgery in the head and neck area results in the contamination of the wounds with saliva rich in virulent organisms, we propose that preoperative radiation be discontinued in favor of postoperative radiation.