In order to obtain an appropriate tissue model to study human diabetes we isolated islet cells from pancreata obtained from brain-dead, heart-beating kidney donor subjects by collagenase dispersion and tissue culture. The presence of viable islet cells was confirmed by both immunofluorescence staining and hormone release experiments. Insulin and somatostatin release were determined on culture day 3 or 4 when amylase measurements indicated an absence of functional exocrine cells. Glucose, alpha-ketoisocaproic acid, theophylline, glucagon, and tolbutamide each stimulated insulin release 2- to 3-fold and somatostatin release 1.5- to 2-fold. Epinephrine and somatostatin both inhibited glucose-stimulated insulin release. Successful subculture of islet cells was achieved after dispersion of primary cultures with dispase. Subcultured islet cells released insulin into the medium during a subsequent 8-day period and when challenged with glucose responded with a 1.6-fold increase in insulin output. Cells cultured on glass coverslips were used to detect, by indirect immunofluorescence, islet cell surface antibodies (ICSA) in the sera of patients with insulin-dependent diabetes mellitus. Of 15 sera from patients with newly diagnosed insulin-dependent diabetes mellitus 9 were ICSA positive, whereas all of 10 control sera were negative; in contrast, using rat insulinoma cells only 4 diabetic sera were positive, as well as 2 control sera. These findings demonstrate the functional viability of adult human islet cells in primary and secondary culture. Cultured human islet cells are a novel, sensitive, and specific system for detecting ICSA and for studying autoimmune effects, and provide a potential source of islet cells for transplantation.