We describe an analysis for propranolol in plasma, with use of reversed-phase "high-pressure" liquid chromatography and fluorescence detection. Pronethalol is used as the internal standard. The procedure, which involves extraction into an organic solvent, evaporation, and clean-up by micro-scale back extraction from hexane into an aqueous phase, is specific and sensitive. The detection limit is less than 6 microgram/L (2.3 X 10(-8) mol/L). Within-day and between-day coefficients of variation are 1.8 and 4.4%, respectively. Commonly used drugs, including procainamide, N-acetylprocainamide, and quinidine, do not interfere.