BRL 49653C is a highly potent and orally active anti-diabetic thiazolidinedione compound. The thiazolidinediones such as BRL 49653C represent a novel class of compounds that act as "insulin sensitizers" in target tissues. Unlike sulphonylureas, BRL 49653C improves the sensitivity of muscle and liver to insulin. An agent that enhances insulin sensitivity may be effective in regulating elevated blood glucose in patients with NIDDM and theoretically may be beneficial in reducing the frequency and severity of morbid complications of this disease. BRL 49653C does not increase pancreatic insulin secretion; therefore, treatment with BRL 49653C should not have the potential to exhaust pancreatic function, or produce the untoward effect of hypoglycemia (a potential complication of treatment with sulphonylureas).