Studies of individual cell types in the islets of Langerhans are complicated by the cells' functional coupling by gap junctions and paracrine interaction. Access to purified alpha and beta cells is therefore desirable. We present a simplified and optimized method for fluorescence-activated cell sorting of endocrine pancreatic rat islets. For dispersion of the islets, dispase was superior to trypsin, as the number of vital single cells was higher (1·1 ± 0·1 × 103 vs 0·6 ± 0·1 × 103/islet, P2+ concentration although both glucose- and arginine-induced insulin secretion was much reduced. We conclude that alpha cells are necessary for insulin secretion but not for glucose sensing. Journal of Endocrinology (1996) 149, 145–154