Fifteen Holstein cows were treated with two doses of 25 mg of a prostaglandin F(2)alpha (PGF(2)alpha as dinoprost tromethamine) administered intramuscularly 11 days apart. The cows were then divided into three groups and inseminated either at 72, 80 or 72 and 96 hours after the second dose of PGF(2)alpha. Thirteen cows ovulated after the second prostaglandin treatment. Eight cows were diagnosed pregnant by rectal palpation 42 days after insemination but only five calved. PGF(2)alpha induced luteolysis in cows with active corpora lutea as evidenced by the dramatic decreases in the plasma progesterone concentrations after treatment. In contrast, following PGF(2)alpha administration to cows in follicular or late luteal phase the concentrations of plasma progesterone either increased gradually or remained low for several days before increasing to maximal levels. The ovulatory rate after the two doses of PGF(2)alpha11 days apart was high. However, the pregnancy rate after this treatment was influenced by other factors including abnormal ovarian function.