The effects of unilateral ovariectomy, unilateral hysterectomy or both an ovarian function were investigated in pigs at day 25 of pregnancy. Removal of 1 ovary during early pregnancy (day 5) resulted in increased ovarian and corpora lutea weight and larger graafian follicles in the remaining ovary. Total progesterone, DNA and RNA content of these individual corpora lutea were higher than those found in corpora lutea of animals with 2 ovaries. Nucleic acid content indicated that increased corpora lutea weight following removal of 1 ovary resulted from an increase in cell number. Total progesterone, RNA and DNA content of corpora lutea were higher in animals with 2 ovaries. However, the concentrations of progesterone, RNA and DNA in luteal tissue were not affected by removing 1 ovary, 1 uterine horn or both. Reduction of the number of embryos by removal of 1 uterine horn had no significant effect on these parameters.