In this method for measuring nifedipine, a calcium-channel inhibitor now widely used in the treatment of cardiovascular disease, the drug is extracted from plasma under basic conditions into toluene, and an aliquot of the extract is injected directly into a gas chromatograph equipped with an OV-101 column and an electron-capture detector. The standard curve is linear between 1 and 100 micrograms/L; the assay measures not only nifedipine, but also a major metabolic product (found only after oral administration of the parent drug) and photodegradation products. The procedure is rapid and adequately sensitive for routine use in clinical monitoring of nifedipine in plasma.