Extracts of Momordica charantia fruit pulp, seed, and whole plant were tested for their hypoglycemic effects on normal and diabetic rat models. The results show that during the oral glucose tolerance test the peak blood glucose values in rats are obtained much earlier (15-45 min) than in human subjects (around 60 min). Pulp juice of M. charantia lowered fasting blood glucose levels in normal rats (p < 0.05 at 120 min); the effect was more pronounced with the saponin-free methanol extract of the pulp juice (p < 0.05 at 60 min and p < 0.01 at 120 min). The pulp juice also had a significant hypoglycemic effect in the glucose-fed normal rats when the extract was fed 45 minutes before the oral glucose load [percentage increments over basal value (M +/- SE): 85 +/- 10 in the control group vs. 54 +/- 7 in the pulp juice group, p < 0.01]. In the IDDM model rats the pulp juice had no significant effect on blood glucose levels either in fasting or postprandial states. In the NIDDM model rats the saponin-free methanol extract of juice produced a significant hypoglycemic effect both in fasting (p < 0.05 at 120 min) and in postprandial states (sum of percentage increments over basal value: 140 +/- 26 in the control vs. 71 +/- 7 in the pulp juice group, p < 0.05). Methanol extracts of seed and of whole plant, and saponin-free methanol extract of whole plant produced no hypoglycemic effects in normal or IDDM model rats either in fasting or in postprandial states.(ABSTRACT TRUNCATED AT 250 WORDS)