This radial compression liquid-chromatographic assay for propranolol in plasma is rapid, reproducible, and suitable for use in routine monitoring. A 10-micron particle, 8 mm X 10 cm CN cartridge is used in conjunction with a radial compression separation system. The mobile phase is monobasic sodium phosphate (pH 3) solution/methanol/acetonitrile (760/84/156 by vol), the flow rate 6 mL/min. Propranolol was detected by use of a spectrofluorometer equipped with a 20-microL flow-through cell, at excitation and emission wavelengths of 250 and 336 nm. The retention times for propranolol and metoprolol (the internal standard) are 3.13 and 1.42 min, respectively. A one-step extraction with chloroform yields "clean" chromatograms, with greater than 90% of the drug being analytically accounted for. Under these conditions, results are precise and accurate. Currently we are using this method to monitor propranolol in hypertensive neonates. Data on changes in the concentrations of propranolol in plasma with time are presented for one such patient.