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.