1,2,3,4-tetrahydrocarbazole (CAR) has been synthesized over H-ZSM-12, H-beta, H-mordenite, H-Y, H-ZSM-22, H-EU-1, H-ZSM-5 and acetic acid by Fisher's method using phenylhydrazine and cyclohexanone. H-Y is more active than the other zeolites studied for the synthesis of CAR. The influence of different parameters such as the duration of the run, catalyst concentration, reaction temperature and molar ratios of the reactants in the synthesis of CAR are also studied. A number of arylhydrazines such as o-tolylhydrazine, p-tolylhydrazine and 1,1-diphenylhydrazine and cyclic ketones such as cyclopentanone, cyclohexanone and 3-methylcyclohexanone have also been taken to study the effect of substitution in phenylhydrazine and the size of the cyclic ketones in the reaction. The yields of indoles correlated with the degree of substitution of the reactants and products, and the limitations imposed on diffusion through zeolite pores.