A highly sensitive and specific radioimmunoassay (RIA) was developed for analyzing somatostatin (SRIF-LI). The monkey pancreas was lyophilized and extracted with 2N acetic acid. The content and composition of immunoreactive somatostatin in monkey pancreas were then evaluated by chromatography process and RIA. The concentration of SRIF-LI in monkey pancreas was around 513.8 ng/g dry weight. At least 3 components of SRIF-LI were detected in pancreatic extracts. The major component of SRIF-LI (about 92%) was SS-14, and other two were SS-28 and a form bigger than SS-28.