SK&F 82526, a benzazepine with a catechol moiety, is a potent, specific renal vasodilator. The method described here for its determination in plasma uses an ethyl acetate extraction and an ether wash, followed by high-performance liquid chromatographic analysis with electrochemical detection. The detection limit is 160 pM. The method was proven accurate, precise and linear over three orders of magnitude (at plasma concentrations ranging from 50 pg/ml to 50 ng/ml). It has been successfully used for plasma determinations of SK&F 82526 in human volunteers following an oral dose of 25-100 mg.