Compounds of 5-benzothiazole-a-alkylacetic acid with substitutions at the 2 position and/or the alkyl function were synthesized and their pharmacological activities studied. Introduction of a methyl group a to the acetic acid function of 2-phenyl-5-benzothiazoleacetic acid lowered toxicity and enhanced antiinflammatory activity relative to that of phenylbutazone employed as a standard.