The predominant cause of death of cancer patients is growth and metastasis of their tumors. By targeting signal transduction pathways as sites of therapeutic intervention, we have identified a novel anticancer drug carboxyamidotriazole (CAI). A straight-forward and reliable method of detection and quantitation of human CAI plasma levels using solid-phase organic extraction followed by isocratic reversed-phase chromatography is now reported. This assay detected CAI over the concentration range 0.04-10.0 micrograms/ml, which brackets the range shown to be physiologically and biochemically effective. Linearity was demonstrated by linear regression analysis of calibration curves (r2 = 0.999). Equivalence of recovery of extracted versus non-extracted CAI over a broad concentration range was demonstrated (r2 = 0.998, coefficients of variability < 10%). The method was applied to quantitate CAI plasma levels from patients now entered on the Phase I clinical trial underway at the National Cancer Institute.