Previously we reported that intestinal cells contain estrogen receptors, and that 17 beta-estradiol enhanced calcium uptake by these cells in vitro. The current study was undertaken to examine the in vivo effects of 17 beta-estradiol on intestinal absorption of calcium and phosphorus. Three groups of rats were studied. Group 1 received solvent vehicle. Groups 2 and 3 received 5 micrograms and 40 micrograms 17 beta-estradiol/kg body weight/day, respectively, for 21 days. Hormone and solvent vehicle injections were given subcutaneously. Rats were fed a Teklad diet containing 0.4% Ca, 0.3% P and 3.0 U vitamin D/g during the study. Intestinal absorption of calcium and phosphorus was assessed over a 5-day period from day 15-19. Carmine red (25 mg/100 g diet) was added to the rat feed to mark the beginning and end of fecal collections. Administration of 17 beta-estradiol caused an increase in intestinal absorption of calcium and phosphorus. The increase was significant only for calcium, and in the animals that received high-dose 17 beta-estradiol (P < 0.05). Serum calcium and phosphorus levels were significantly greater in 17 beta-estradiol treated than in control animals. The urinary excretion of calcium and phosphorus was also increased in a dose-dependent manner by 17 beta-estradiol, and was significant for both calcium and phosphorus in animals that received high-dose 17 beta-estradiol (P < 0.05). In contrast, 17 beta-estradiol treatment did not significantly alter the serum levels of parathyroid hormone and 1,25(OH)2 vitamin D. These findings indicate that estrogen administration promotes intestinal absorption of calcium in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)