Intracellular adenosine triphosphate (ATP) is the primary energy unit of living cells, and can be quantitated by measuring the light generated with luciferase-luciferin reagent in a luminometer. The use of an ATP-bioluminescence assay, to determine tumor cell viability after exposure to chemotherapeutic agents, has been adapted to test tumor chemosensitivity in vitro. This presentation will illustrate the method of the ATP-chemosensitivity assay (ATP-CSA) using an ovarian cancer cell line NIHL:OVCAR-3 as an example and present preliminary data on 54/56 successful in vitro ATP-CSA's from 46 patients with pelvic malignancies. Fresh human tumor specimens were generally tested for single and combined drug effects at two drug concentrations (0.2 X and 1 X peak plasma concentrations). Correlation of in vitro drug sensitivity and in vivo patient response was obtained for 23 treatment regimens in 22 patients with ovarian carcinoma. The true positive rate was 100% and the true negative rate 66.7%. Our data demonstrate (a) that the ATP-CSA, measuring total cell viability, is a feasible in vitro assay for human tumor drug testing and (b) that specific criteria of in vitro chemosensitivity for this assay need to be defined by further studies, for single and combined drug exposure at different concentrations, to permit a meaningful correlation with in vivo clinical response.