A method has been developed to simultaneously determine aspirin and salicylic acid in rat whole blood. Aspirin and salicylic acid are extracted from acidified whole blood into a 50/50 v/v ethylacetate/butylchloride organic solvent system containing internal standard (meta-anisic acid). Following controlled evaporation of the organic extract under partial vacuum, the dried residue is reconstituted with mobile phase. Chromatography is ion suppression reverse phase on a 5 μm octyldecasiland column with detection by UV absorbance at 280 nm. In this method, the procedure of blood centrifugation for plasma preparation is eliminated. Therefore, the blood volume required is decreased and the sensitivity of analysis is considerably increased. Concentrations of aspirin as low as 0.5 mcg/ml and salicyclic acid as low as 1.5 mcg/ml can be quantitated in as little as 100 μl of whole blood.