The effect of Trembolone acetate was studied in fattening cull cows. Twenty black and white cows were used. Ten cows were implanted with 300 mg of Trembolone acetate and the other ten were the control group. Both groups stayed eight weeks in the barn, where they had pasture silage ad. Iibitum + 1 kg of rapeseed meal/cow/day The second period was on pasture, during 10 weeks. Implanted cows during the barn period, showed a better daily weight gain (0.82 vs 0.68; P < 0.05). During the pasture period, gain ditferences were proportionally smaller (1.58 vs 1.45 kg/day; P < 0.10). lmplanted cows showed a higher efficiency than untreated controls (13.5 vs 16.3 kg DM/kg L.W.). There were no statistical differences in the carcass characteristics, relation between quarters and yield.