The ability of the pancreatic B-cell to synthesize and secrete insulin in tissue culture has been established in several studies, most of which involved culture of different preparations of fetal pancreas. In all these studies, however, a substantial admixture of non-endocrine cells complicated a more detailed study of the islet cell. In order to overcome these difficulties we have developed a method for in vitro culture of isolated pancreatic islets, which is well suited for evaluating both morphologic and metabolic changes of the islet cells induced during prolonged culture periods. The present paper will review briefly the work performed on culture of isolated pancreatic islets with special attention to the influence of different culture conditions on the in vitro survival of the explanted islet specimens. It was shown that various kinds of pancreatic islet specimen including isolated human pancreatic islets can be successfully cultured provided that they do not exceed an upper critical size limit and that calf serum is added to the culture medium. The functional characteristics of the cultured islet cells were markedly influenced by the glucose concentration of the culture medium. Thus several signs of hyperactivity were observed in islet cells subjected to a high glucose concentration, while exposure for one week to a subnormal extracellular glucose concentration led to an impairment of their specific functions. Furthermore it was found that L-leucine and B-hydroxybutyric acid were able to replace glucose as a long-term stimulus of the insulin biosynthesis, while succinate and HB 419 did not share this property.