Physicians conducted complete 24-hour serum profiles of cholecystokinin in 9 22-31 year old women attending a local health care center in Karolinska, Sweden before they began taking combined oral contraceptives (OCs) and 2-3 months after taking the OCs to determine whether changes occur in cholecystokinin values when women take OCs. The physicians used a portable, battery-charged excentric pump to collect 5 ml blood samples every 30 minutes from an antecubital vein during the women's normal daily activities. They also saw to the recording of their food intake and activities. The radioimmunoassay revealed that the serum 24- hour profiles of cholecystokinin values were consistently lower after the women began taking the OCs than before (p.001). The values were at their closest at noon-2 pm and greatest at 2-4 pm. Research has shown reduced food intake in both laboratory animals and humans when researchers administer cholecystokinin. Yet, if cholecystokinin secretion is suppressed, food intake increases. These findings suggest that reduced cholecystokinin secretion during OC administration may explain increased appetite and weight gain in women taking OCs. Additional research is necessary to determine the significance of this effect and its mechanism.