Six young (1.5–2.5 yr) and six mature (3–6 yr) bulls were ejaculated once weekly for 4 weeks. Two ejacula were taken after three or four false mounts and two were taken during the first mount (no false mounts). Sera prepared from tail vein blood collected 30 min before and 5 and 30 mm after each ejaculation were assayed for prolactin, luteinizing hormone (LH), and growth hormone (GH). Sexual preparation increased (p < .01) seminal volume and total sperm per ejaculum. Before ejaculation, levels of serum prolactin averaged 10.8 ng/ml. Serum prolactin increased (p < .01) to 59.0 ng/ml 5 min after ejaculation and decreased to 38.3 ng/ml 30 min after ejaculation. Levels of LH, which averaged 1.18, 1.33, and 1.05 ng/ml in samples taken at comparable intervals, did not differ significantly. Growth hormone increased (p < .01) from 4.1 ng/ml before ejaculation to 8.1 ng/ml 5 min after ejaculation and returned to pre-ejaculation values by 30 min after ejaculation. Neither age nor sexual preparation affected levels of prolactin or LH. In contrast, GH was higher (p < .01) in older than in younger bulls, and higher (p < .01) after sexual preparation. We conclude that stimuli associated with ejaculation cause release of GH and prolactin, and possibly LH, but prolactin is released in greater quantity than LH or GH.