Immature cumulus oocyte complexes (COCs) were aspirated from ovarian follicles of slaughtered cow and matured for 24 h in TCM 199 medium with hormones. Eighty-five percent of oocytes matured with subsequent abstriction of the polar body. Matured COCs were then inseminated with frozen-thawed semen (2 x 10(6)/mL final concentration). Eighteen hours after insemination, fertilized COCs were vortexed, washed, and cultured to the pronuclear stage and syngamy (24-36 h postinsemination) and fixed for TEM. Unfixed embryos achieved a cleavage rate of 54%, with 29% developing to blastocysts. Fertilization was confirmed by TEM. Examination of fertilized bipronuclear ova revealed the presence of a sperm aster associated with sperm midpieces, tails, and male pronuclei in several embryos. Further examination of embryos at syngamy showed centrioles at one pole of the first mitotic bipolar spindle in two embryos. Since the mature oocyte at metaphase II has no centrioles at spindly poles, this centriole was most likely derived from the sperm, which has a single proximal centriole associated with pericentriolar material in its neck region, like most mammalian sperm. Tripronuclear ova produced disorganized bipolar spindles or, rarely, tripolar spindles. Bovine embryos, too, follow Boveri's rule of paternal inheritance as in man and most animals. It is possible that both paternal centrosomes (centrioles) and maternal centrosomes are involved in the organization of bipolar spindles in these embryos, quite unlike the mouse embryo where maternal centrosomes seem to organize the first mitotic spindle. The bovine embryo appears to be an appropriate model to study centriolar inheritance.