A combination of gel-permeation HPLC, affinity chromatography on heparin-Sepharose, gel electrophoresis, and estimation of inhibitory activity showed that effect of low-frequency ultrasound (26 W/cm(2), 37 degrees C, pH 7.4) on homogeneous antithrombin III was accompanied by formation of aggregates and a latent form of serpin. Heparin and pentosan polysulfate stabilized antithrombin III; this resulted in decrease in ultrasonic-induced formation of the aggregate and latent forms. The influence of ultrasound was not accompanied by significant changes in the contents of non-activated blood coagulation factors in the PPSB complex.