The combination of GNRH and prostaglandin F2<FONT FACE=Symbol>a</FONT> allows the control of the luteal phase and the follicular dynamic that coexist in the ovary, facilitating precise oestrus synchronisation schemes. The study was intended to characterise the reproductive response to the use of this combination for an oestrus detection program. The study considered 423 clinically sound dairy cows, from two herds, 1 to 7 calvings and adjusted production levels from 7.500 to 12.500 Kg. Cows were confined under a free-stall system and both herds were under a sanitary and nutritional control program. Since 50 days after calving, cows received 10 µg of buserelin and those having a corpus luteum, based on ultrasound assessment 7 days later, received 0.75 mg of tiaprost. At the moment of tiaprost administration and 72 h later, milk was collected for progesterone by RIA. The results showed that 90.7% (206/227) cows had a functional corpus luteum at the moment of prostaglandin administration, 93.7% (193/206) responded with luteolysis, and that 85.0% (164/193) showed oestrus behaviour. The interval to the oestrus was 66±15.2 h with 93.9% of cows presenting oestrus between days 2 and 4, with a high percentage (54.9%) presenting oestrus on day 3 after tiaprost administration. Finally, the conception rate was similar to the untreated controls (55.4% (144/269) vs. 50.3% (82/163) for treated vs. untreated respectively. No differences were found between herds in any parameter considered in the study. Based on the results, it can be concluded that the combination of GnRH and PGF2<FONT FACE=Symbol>a </FONT>can be an effective alternative to approach the problem of estrus detection in confined dairy herds