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Two experiments were performed on seasonally anovular Merino ewes to determine the intervals between time of introduction of rams, the preovulatory surge of LH and the first ovulation. Ovulation was determined by laparoscopy and LH was measured by solid phase radioimmunoassay. In Experiment 1 the interval between the introduction of rams and the beginning of the LH surge was 27 ± 4 h (mean ± S.E., range 6–52 h), and in Experiment 2 probit analysis shows that 50% of teased ewes ovulated within 41 h of being exposed to rams.