We examined the pharmacokinetics of theophylline in two types of experimental diabetic rats, streptozotocin-induced diabetic (STZ) rats with insulin dependent diabetes mellitus, and a genetic model of non-obese Goto-Kakizaki (GK) rats with non insulin dependent diabetes mellitus. After the rats were administered theophylline either intravenously or orally plasma was taken for a pharmacokinetic study. There were no significant differences in the pharmacokinetics of theophylline in the STZ rats compared with those of the controls. On the other hand, a delayed elimination process and absorption rate of theophylline were observed in GK rats in comparison to those of the controls. There findings suggest that two different phamacokinetics of theophylline exist depending on the two types of diabetic rats.