Local anesthetics may influence cell membrane structure and permeability. An established human melanoma cell line (SHG) derived from malignant ascites was used to evaluate the growth-inhibitory effects of local anesthetics (procaine and lidocaine) as well as of doxorubicin at incubation temperatures of 37.5 degrees C and 40 degrees C. In this system, procaine and lidocaine inhibited growth at 0.82 mg/ml and doxorubicin inhibited growth at 28 ng/ml. Noninhibitory concentrations of procaine (0.64 mg/ml) when combined with noninhibitory concentrations of doxorubicin (10 ng/ml) resulted in marked growth inhibition. Incubating temperatures of 40 degrees C enhanced all effects of procaine and doxorubicin on cell growth. These results suggest that clinically achievable concentrations of local anesthetics enhance doxorubicin cytotoxicity.