Quantitation of plasminogen activators present in tissue may depend to a large extent on the extraction procedure used to solubilize the enzymes. Potassium thiocyanate solution is known to be an efficient solubilizer, but it can inhibit assay systems other than fibrin plates. An equally effective acetate-detergent extractant is reported here which can be used with the highly sensitive azocaseinolytic assay procedure. The results indicate that a three-fold increase in activator activity can be extracted from selected tissues relative to that previously reported for a phosphate-detergent extractant. The extraction medium contains 75 mM K acetate, 0.3 M NaCl, 0.1 M L-arginine, 10 mM EDTA, 0.25% Triton X-100, final pH 4.2.