The influence of Adriamycin and Actinomycin D on the expression of residual damage following irradiation of mouse thorax was evaluated. Drugs were given i.v. at various times starting on the same day, up to 3 months after irradiation, and the mortality from lung damage up to 160 days or epilation up to 98 days after irradiation were noted. Adriamycin (1.2 mg/kg in two equal doses), which on its own did not cause pneumonitic deaths, did so when combined with doses of local thoracic radiation as small as 6 Gy. The dose effect factor was greater if Adriamycin was given at 1 or 2 months (1.68) rather than on the same day (1.49). A reduction in the latent period to death was also observed with a minimum period of 50-60 days after irradiation rather than the normal 80-160 days. Adriamycin enhanced the epilation response to radiation, but only at or above threshold radiation doses. There was no reduction in the latency. Actinomycin D had no dose-modifying effects on the radiation response of both lung and hair follicles. The interaction between irradiation and Adriamycin seen when the interval between the two modalities is long, as it was in this study, may be mechanistically similar to the "radiation recall" phenomenon described in the clinic.