The distribution and localization of acid stable trypsin inhibitor(ASTI) in malignant human tissues from six different organs were examined using immunohistochemica1 techniques. ASTI immunoreactivity was detected in most of the malignant tissues examined. It was found that ASTI existed not only in the extracellular space but also in the cytoplasm of the malignant cells. Results of immunohistochemical studies suggest that the malignant cells themselves could produce ASTL
