During the winter of the season 1984/85, a 70 days trial was conducted, with grass hay, treated with anhydrous ammon'la (1.5% D.M.), using the "stack method". Eighteen Hereford steers (280 kg initially) were used to compare the following treatments: I. Hay bailed 1 day after cutting, with immediate application (27.12.84) of NH3 (60% D.M.); II. Hay bailed in a conventional way plus NH3 application (20.02.85); and III. Hay bailed conventionally (check). AII treatments were fed in a yard; they were supplemented with 3 kg of bar:ley and 0.6 kg of rapeseed meal, plus mineral salts (0.116 kg/animal/day). The hay analysis were 66.6,82.7, and 79.4% D.M.; 13.2, 13.3, and 6.3% total protein; 55.3,54.8, and 47.7% DIV and 36.4, 37.4, and 37.0% fiber, respectively, for treatments I, II, and III. Liveweight gains of steers were 0.803, 0.837, and 0.748 kg/ day (P > 0.05). Hay inta ke was 6.65,5.84, and 5.58 kg/day, respectively. Good effects were observed on the nutritive value, but these were not reflected on the steers' liveweight gains.