Three new 4-amino-2-alkylsulfonyl benzoi:: acids, namely, 4-amino-2-methylsulfonyl benzoic acid, 4-amino-2-ethylsulfonyl benzoic acid and 4-amino-2-n-propylsulfonyl benzoic acid, have been studied for in vitro in human tuberculosis, hoping that they would surpass the p-amino- salicylic acid in activity. Contrary to our expectations, however, these new compounds have been found to be far less active than the p-amino-salicylic acid itself. The 4-amino-2-n-propyl-sulfonyl benzoic acid possesses an activity in the order of 10-3 in concentration, while the other two compounds require still higher concentrations.