The effect of chemotherapeutic and/or immunotherapeutic drugs on cells obtained from primarily cultured renal cell carcinoma (RCC) was investigated in a microcalorimetric study. This method enables the detection of heat flow in the submicrowatt range, which corresponds to a 1.0x10(-6) degrees C temperature change. The thermal power of 10 individual cell lines from patients with advanced RCC was measured by incubating cells with or without anti-cancer drugs (5-fluorouracil, interferon-alpha-2a, interleukin-2). Using a 4-channel microcalorimeter, it could be shown, that the combination of 5-FU with IFN-alpha-2a or IFN-alpha-2a plus IL-2 led to a significant reduction in thermal cell activity, compared with the addition of 5-FU on its own. These microcalorimetric observations appear to reflect the anti-neoplastic properties of the drugs tested in this study when compared with the findings in a calorimetric assay (MTT-assay).