Technical Abstract: We tested the hypotheses that interval from urine exposure to resumption of luteal activity and proportions of cows that resume luteal activity by the end of the urine-exposure period do not differ between cows exposed to mature bull urine or steer urine. Thirty-eight Angus x Hereford cows, four mature A x H bulls and four ten-mo-old A x H steers were used in this study. Cows were stratified by calving date, cow BW, calf BW, calf sex, dystocia score, and BCS, and fitted with a controlled urine delivery device (CUDD) two wk before the start of treatments, and assigned randomly to be exposed continuously (24h/d) to bull urine (BUE; n = 19) or steer urine (SUE; n = 19) beginning 40 d after calving. Urine was collected from bulls and steers every third d of the experiment. Blood samples were collected from cows starting on d 0 and every third d thereafter until end of the exposure period (~64 d). Likewise, CUDD were filled and refilled on the same schedule. Serum was assayed for progesterone by RIA. Neither interval from urine exposure to resumption of luteal activity nor proportions of cows that resumed luteal activity during the urine-exposure period differed between BUE and SUE cows. We conclude that continuous exposure to mature bull urine does not affect resumption of luteal activity of primiparous, suckled beef cows.