A spectrophotofluorometric method is described for the quantitative analysis of coumarin, umbelliferone, and mixtures thereof in whole blood. The two drugs were selectively isolated from blood by solvent extraction. Analysis of the isolated coumarin was based on the measurement of the fluorophore at activation and emission wavelengths of 361 and 491 nm, respectively. The fluorophore was obtained by irradiating an alkaline methanolic solution of the drug with UV light. A linear relationship between fluorescence and concentration existed over the concentration range of 0.02-0.2 mug of coumarin/ml. A mean recovery value of 94.8% was obtained from whole blood. The isolated umbelliferone was determined according to established methods at activation and emission wavelengths of 370 and 450 nm, respectively, and the limit of detection was 10 times more sensitive than previously reported. A linearity response was obtained between 1 and 10 ng of umbelliferone/ml. Good recovery data for mixtures of coumarin and umbelliferone in whole blood were obtained.