Twenty-four Hereford oxen were used in a 2 X 2 factorial arrangement of treatments in order to investigate the response in terms of gain and efficiency of feed conversion to the inclusion of monensin and sodium bicarbonate (NaHCO3) in a feedlot ration. Monensin was added at a rate of 34 ppm (OM basis) whereas NaHCO3) was included at a rate of 1%, in a basal ration which already contained 1% limestone (CaCO3). Monensin did not influence rate of live mass gain, but it did markedly depress feed intake, particularly during the early phases of the experiment. The net effect was 16,4% improvement in efficiency of feed conversion. Carcase dressing percentage was not significantly influenced. Sodium bicarbonate had no significant influence on rate of gain, but it did have a slight depressing effect on feed intake and a small decrease in efficiency of feed conversion was observed. Vitamin A injections had no measurable effect on feedlot gain.