JOHN P. BALIOSUnder the supervision of Professor Richard C. Wahlstrom Experiments designed to study the potentiation of antibiotic in swine were conducted over a two-year period.During the two years, 344 crossbred pigs were used ?n three separate experiments to study the effect of calcium sources and levels, sulfate sources and levels, and phosphorus levels in diets containing different levels of Chlortetracycline. The first experiment was divided into three twoweek periods. During the first two weeks 50 g/ton of Chlortetracycline in the diets increased gain of pigs from 0.68 to 0.72 kg. per day. Pigs fed diets containing Chlortetracycline gained significantly faster when the source of calcium was sulfate rather than carbonate. In the second period, pigs receiving a higher calcium diet with antibiotic grew significantly faster than those fed a low calcium diet. During the third two-week period pigs fed a calcium carbonate diet achieved gains significantly greater than those fed a calcium sulfate diet. On an accumulative basis (0-6 weeks) there were no significant differ-