Cultured rat lung fibroblasts (F-cells) and Walker rat carcinoma cells (WRC-cells) labeled with 51Cr were exposed to the following antitumor drugs alone or with O3: carmustine (BCNU), doxorubicin (Dox), cisplatin (CPt), mitomycin C (Mit C) or vitamin K3 (Vit K). Release of 51Cr (cell injury) was greater for F-cells than WRC-cells with any single treatment. Pretreatment with any drug (400 microM), except for Vit K with WRC-cells, did not significantly increase O3-induced loss of 51Cr. Co-exposure of F-cells to drugs and O3 resulted in a marked potentiation of O3-induced injury with Vit K, and an inhibition with Dox.