The aim of the present study was to investigate whether plasma levels of gastrin, somatostatin, insulin, oxytocin, VIP and blood glucose levels vary during the menstrual cycle. Therefore, 19 healthy menstruating women (5 of whom were on low-dose oral contraceptives, o.c.) were blood sampled every second to third day during the menstrual cycle. Hormone levels were measured with radio-immunoassay. Gastrin, insulin, VIP and blood sugar levels remained unchanged during the menstrual cycle. Mean somatostatin levels were significantly lower in women receiving o.c. than in women without such medication (p less than 0.05). In women on o.c., somatostatin concentrations were also significantly lower during the menstrual week, than during the rest of the period (p less than 0.01), but in women without o.c., no such change occurred. Mean oxytocin levels were significantly higher in women on o.c. (p less than 0.001) and in these women, oxytocin levels recorded during the menstrual week were significantly lower than during the rest of the period (p less than 0.02). Systolic and diastolic blood pressure values were also significantly higher in women on o.c. (p less than 0.05 and p less than 0.01). In conclusion, these data show that basal plasma concentrations of gastrin, somatostatin, VIP, insulin and glucagon do not vary during the menstrual cycle. However, ingestion of low-dose oral contraceptives causes a significant decrease of somatostatin concentrations and a significant increase in oxytocin levels, suggesting that low doses of estrogens and/or gestagens may influence digestive and metabolic processes.