Abstract: Slow cortex response to several frequencies was recorded in guinea pigs bofore and after intense impulse noise exposure. Guinea pigs were decapitated 90 minutes after the exposure. Besides scanning electron microscopic examination of cochleas, activities of Na⁺-K⁺-ATPase and SDH in the stria vascularis（SV） corresponding to 4 kHz were studied with histochemical methods under light microscope. Densities of the histochemical reaction products and cross sections of the SV were measured with Image Analysis System. Activities of Na⁺-K⁺-ATPase and SDH in the SV decreased significantly in PTS group（P＜0.01, P＜0.05）. There was no significant change in TTS group. It is suggested that the decrease of Na⁺-K⁺-ATPase and SDH in the SV may contribute to remarkable hearing threshold shift besides mechanical destruction by noise. Metabolic disturbance may aggravate hair cell damage. Direct damage of the SV caused by intense noise may be one of the causes of PTS.