The objective of this experiment was to evaluate the effect of the aplication of prostaglandin (PGF2a) sincronization, in the reproductive performance of high producing dairy cows. 120 Holstein- Friesian cows were randomly allotted to one of two treatments (Control and Experimental). Both treatments were fed the same diet (TMR) during 180 days. The diet had 2,9 Mcal of Metabolizable Energy/kg DM and 17% CP. Cows in the Control group were bred when they presented heat after 45 days of a voluntary wait period. Cows in the Experimental group received a first application of PGF2a, after 45 days of the voluntary wait period and were bred when they presented a heat. If they did not show estrous after the first application, they received a second doses 14 days later, and if they still did not show heat, they received a third inyection of PGF2a, 14 days later. Heat detection was done twice a day, early in the morning and late in the evening. The breeding system was AM/PM. Reproductive performance in both groups was compared using the following parameters: days between calving and first heat, days between calving and first service, days between calving and pregnancy (days open, DA) and conception rate (IC). Reproductive performance was better in the experimental group. PGF2a improved heat detection, because heat was more evident and more cows became into in estrous. Grouping animals that showed heat behaviour also improved heat detection. The high heat detection rate improved fertility because more cows were detected in the optimum moment of heat to be bred. First service fertility was better because follicules were developed in a positive energy balance period. As a consequence of this, DA and IC improved.