Productivity and production distribution of the natural pasture at two localities (Peleo, lat. 37º 49' S, long. 73º 20' W and Quiapo, lat. 37º 31‘S, long. 73° 31' W) were studied, during the seasons 1977/78 (July fo April) and 1978/79 (July to February), with and without NPK (32-90-50 kg/ha of N, P2O5 and K2O, respectively). Through periodical cuttings, the accumulated DM. was measured, using an exclusion system stablished at the beginning of the experiments. Qn January 1978, regrowth following the spring cuttings was measured. Botanical composition was determined in alI the cut material. Accumulated D.M. values were fitted, for each location, treatment and season, using the function y = A/1 + be-ax The maximum accumulation, estimated for the different locations, seasons, and treatments, varied between 3.5 and 7.5 Ton MS/ha and was obtained in January. Maximum rate of daily growth varied between 40 and75 kg/ha and occurred from September to October. All the cases showed positive response to fertilizers, with the exception of the experimet at Quiapo, during 1978/79. Regrowth after cutting decreased as the season advanced, being below 1 Ton/ha from November on. Dry mater loss in situ, afterthe maximum accumulation, reached 50% in April 1977/78. Agrostis spp. was the most frequent grass at Peleco and genera Holcus, Bromus, Lolium, Medicago Plantago and others of the compositae family, the most abundant at Quiapo.