The effect of ovine prolactin on intestinal Ca absorption and placental Ca transfer was studied in pregnant ewes. Six groups of five animals bearing a single fetus were used and injected s.c. daily between days 121 and 135. The first group was given 0.1 microgram ovine prolactin/kg body wt per day, the second 0.1 microgram ovine prolactin/kg body wt per day plus 0.1 microgram 1 alpha-hydroxycholecalciferol (1 alpha-OH-D3)/kg body wt per day, the third 0.1 microgram ovine prolactin/kg body wt per day plus 0.20 units calcitonin/kg body wt per day, the fourth 2 micrograms bromocriptine/kg body wt per day, the fifth 2 micrograms bromocriptine/kg body wt per day plus 0.1 microgram ovine prolactin/kg body wt per day, and the sixth were controls injected with vehicle alone. The intestinal Ca absorption was measured on a duodenal loop tied off in vivo on day 136 and placental Ca transfer was evaluated between days 129 and 136. Ovine prolactin stimulated both intestinal Ca absorption and placental Ca transfer; these effects were further increased by 1 alpha-OH-D3. Calcitonin had no effect on ovine prolactin-stimulated intestinal Ca absorption, but blunted the influence of ovine prolactin on Ca placental transfer. Bromocriptine decreased both intestinal Ca absorption and Ca placental transfer but these effects of bromocriptine were overcome by simultaneous injection of ovine prolactin.