In 1953, Eisner et al.1 reviewed some of the factors that affect the absorption and the blood levels attained after oral administration of various drugs, with particular reference to chlortetracycline, and reported on a study of methods for increasing the absorption of this antibiotic after oral administration in rats and guinea pigs. When certain adjuvants were given simultaneously with oral doses of chlortetracycline or oxytetracycline, serum levels in rats increased up to tenfold. The most effective of these adjuvants was citric acid, but a number of other simple organic acids and sodium monophosphate also enhanced the blood levels of chlortetracycline . . .