A high-performance liquid chromatographic procedure using a fluorescence detector for the analysis of atenolol in plasma and whole blood is described. It employs a simple and rapid method of preparation. Atenolol and metoprolol as the internal standard are chromatographed as ion pairs with heptanesulfonic acid. The method is sensitive and reproducible with accurate detection at concentrations as low as 2 ng/ml in whole blood and plasma, and a coefficient of variation of 4.7% over the range 2 ng/ml to 1000 ng/ml.