The combined effects of continuous low dose rate irradiation (CLDRI) and concurrent infusion of bleomycin, cyclophosphamide, cis-platinum, 5-fluorouracil, actinomycin D, and mitomycin C were studied in the SCC VII/SF tumor, a squamous cell carcinoma and the jejunal crypt cells in the mouse. For the SCC VII/SF tumor, enhanced cell killing was seen with each of the six drugs when infused concurrently with CLDRI; the greatest enhancement was seen with mitomycin C and cis-platinum. For the jejunal crypt cells, enhanced cell killing was seen primarily with bleomycin. At a dose of 20 Gy, the dose effect factor (DEF) ranged from 1.13-1.64 for the SCC VII/SF tumor and 0.92-1.19 for the jejunal crypt cells. Our results suggest a therapeutic gain with concurrent CLDRI and chemotherapy infusion for five of the six chemotherapeutic drugs studied with the exception of bleomycin.