Freshly ejaculated bull semen was centrifuged and spermatozoa were resuspended in modified sperm TALP. Bovine uterine tube epithelial cell monolayers (BUTC) were obtained from cows in the periovulatory phase of estrus. In Experiment 1, sperm aliquots were assigned to culture wells containing either BUTC, BUTC-conditioned TALP, or control TALP. Sperm heads attached to the monolayers within 1 h of co-culture. Attached spermatozoa showed vigorous tail motion. At 5, 8 and 11 h of incubation at 39 degrees C, the percentage of unattached sperm cells with intact acrosome membranes and percentage of motility of these cells was measured. Sperm-BUTC co-cultures were also fixed in situ for electron microscopy. Unattached spermatozoa in co-culture had more (P<0.05) acrosomal membrane loss, showed hyperactive motion and had an overall decrease in motility as compared to sperm cells in control or conditioned medium. Evaluation by electron microscopy showed BUTC attached spermatozoa to behave in the co-culture system similar to reports for spermatozoa found in uterine tubes in vivo. Microvilli of the BUTC appeared to actively entrap the spermatozoa. Mucus-type granules could be seen on acrosomal regions and vesiculation of acrosomal membranes was seen in some cells. In Experiment 2, 43% of the 12 x 10(6) sperm cells added to 2-cm(2) BUTC bound within 4 h of co-culture. By 7 h of co-culture 19% of the previously bound sperm cells had been released from the BUTC. Released cells had limited motility and were mostly dead (73%). Sperm cells remaining on the monolayer at 7 h showed vigorous tail motion and were gradually released from the BUTC over 48 h. Spermatozoa in co-culture interacted with the BUTC in a manner much like that seen in vivo, and sperm capacitation changes were stimulated by this interaction.