The preparation of a series of 1H-imidazol-1-yl-substituted benzo[b]furan-, benzo[b]thiophene-, and indolecarboxylic acids is described. Most of the compounds were potent inhibitors of TxA2 synthetase in vitro, and the distance between the imidazole and carboxylic acid groups was found to be important for optimal potency. The most potent compound in vivo was 6-(1H-imidazol-1-ylmethyl)-3-methylbenzo[b]thiophene-2-carboxylic acid (71), which, in conscious dogs, showed a similar profile of activity to that of dazoxiben (1).