A high-performance liquid chromatographic method for the simultaneous determination of propranolol and 4-hydroxypropranolol in plasma is presented. The method involves plasma extraction at basic pH with ethyl column, and fluorescence detection. The within-run a reversed-phase column coefficient of variation were 3.0-7.1% for propranolol and 5.8-8.3% for 4-hydroxypropranolol. The day-to-day variations were 4.6 and 8.2% for propranolol and 4-hydroxypropranolol, respectively. The method can detect 1 ng of each compound/ml of plasma.