During to 1983-1988 seasons a fattening system of beef production was started at the Remehue Experiment Station. The steers were fed exclusively by pasturing the two first seasons and then they received an energetic supplementation (molasses, 250 kgjhead, approxímately). They did not receive tradítional concentrates. The aim was to evaluate the productivíty of permanent pastures with an annual fertilization of 32 kg/ha of nitrogen and 31,4 kg/ha of phosforus. The botanical composítion of this pasture was predominantly grasses (Lolium sp, Bromus sp, Agrostis sp, Anthoxanthum sp, etc.) and some legumes such as Trifolium repenso The system and was run up for a five years periodo The area was six ha, divided in ten paddocks, the stocking rate was 2.5 frisian-type steers/ha. Each animal had approximately 285 kg of liveweight. In December of every year, animals started in the system at the same time that the old animals got off. Annually 40% of the area was used for forage conservation as silage to be used in the next winter in case no molasse supplements were used. When using this complement, silage was given at the beggining of winter in order to postpone prairie usage. Prairies were used later together with energetic suplements. The average results in two years when no supplements were used and in three years when molasses were used was 504 and 649 L.W.G. kg/ha respectively, the final weights were 470 and 550 kg/head and the annual weight gain in the same period were 202 and 260 kg/ha year. Better economical profit was obtained when energetic supplementation is used. The average gross margin per ha in the two inicial period and in the three final periods with supplements was $83.193 and $110.628/ha respectively. The annual profitabilíty (percentage/year) includying the land was 11.6% without supplement and 14.83% wíth molasses. The price of the land was $450.000/ha ($1990).