[en] Somatostatin binding to its receptor on rat anterior pituitary cell membranes was characterized with (¹²⁵I-Tyr) somatostatin (SRIF). It was found that significant levels of specific ¹²⁵I-SRIF binding occurred at 4⁰C following an overnight incubation with pituitary membranes. A parallel amount of specific binding occurred within 10 minutes at 37⁰C. However, specific binding at 37⁰C decreased rapidly over time such that minimal specific binding was observed by 4 hours at 37⁰C. The rapid decline in specific binding over time at 37⁰C suggested that proteases may be degrading the ¹²⁵I-SRIF, therefore, the effect of various protease inhibitors was evaluated. No specific binding was observed in the presence of serine protease inhibitors such as PMSF, aprotinin, leupeptin, and soybean trypsin inhibitor. In contrast, the presence of 1 mg/ml of bacitracin, an antibiotic that may be acting as a chelating agent, was essential for specific somatostatin receptor binding. A powerful chelator, 1,10-phenoanthroline, was found to increase the specific binding of ¹²⁵I-SRIF, significantly above that achieved in the presence of bacitracin