This chapter describes a method to measure the viability of isolated intact islets of Langerhans from rat pancreas and considers the use of isolated islets and of pancreatic beta-cell lines to study cell viability following culture. The islet isolation method is based on the use of preparations of collagenase to selectively digest the bulk of the exocrine tissue while leaving the endocrine islets intact and separated from their surrounding acini. The islets can be obtained in relatively pure form and are suitable for use in hormone secretion assays as well as for measurement of cell viability. They can be cultured if required and viability maintained for periods of days to weeks. Beta-cell lines are useful for study of the control of cell viability although their secretory capacity is usually altered compared to primary islet cells. Islet cell death can be estimated in a number of ways using either direct or more indirect means. Some methods will distinguish between apoptotic and necrotic death while others offer a more generic index of changes in viability.