A simple procedure is developed for isolation of Langerhans islands (LI) from rat pancreas. Homogenization of pancreatic tissue was carried out using two 'Record' syringes equipped with needles of various diameter. Collagenase was not used in the procedure. After homogenization LI were individually separated using stereomicroscope. The insulin-producing capacity of LI was estimated by assay of immunoreactive insulin content in LI and in the incubation media at 0 degrees and 37 degrees as well as by their reaction to various concentrations of glucose. The procedure enabled to isolate functionally active LI and to study biosynthesis and secretion of insulin in vitro.