Cholera toxin was selected for pharmacologic evaluation by the National Cancer Institute on the basis of antiproliferative activity against small-cell and non-small-cell lung-cancer cell lines. A feature common to the sensitive cell lines was abundant expression of GM1 ganglioside, the cellular receptor for cholera toxin. A sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantitate cholera toxin in biological fluids. A sigmoidal relationship was observed between the cholera toxin plasma concentration and the absorbance at 490 nm (OD490) of the product of horseradish peroxidase-catalyzed oxidation of o-phenylenediamine over the range of 6.25-1,600 ng/ml. Logit transformation of the OD490 data was linear over the entire concentration range and assay variability was less than 25%. Cholera toxin was stable in murine and human whole blood and plasma. Following i.v. administration of 1,500 micrograms/kg to male CD2F1 mice, cholera toxin plasma elimination was described by a two-compartment open model. The half-lives (t1/2 alpha, t1/2 beta), plasma clearance, and steady-state volume of distribution were 0.7 min, 49 min, 24 ml min-1 kg-1 912 ml/kg, respectively. Cholera toxin was not detected in plasma following an s.c. dose of 1,500 micrograms/kg. Urinary recovery following intravenous drug administration was less than 0.1%.