A novel series of N-substituted 3-(1H-imidazol-1-ylmethyl)indole carboxylic acid derivatives were prepared and evaluated for thromboxane A2 (TXA2) synthetase-inhibitory and histaminergic H1-blocking activity. Among the compounds synthesized, indole-6-carboxylic acid derivatives showed higher activities than the other positioal isomers of carboxylic acid. 1-[3-(4-Benzhyrdyl-1-piperazinyl)propyl]-3-(1H-imidazol-1-ylmethyl)-1H-indole-6-carboxylic acid (12) had the strongest thromboxane synthetase inhibitory activity (IC50=5×10-8M) and H1-blocking activity (IC50=8×10-9M).