The Madagascar periwinkle Catharanthus roseus accumulates a number of terpenoid indole alkaloids, some of which have high therapeutic interest. The biotechnological approach with cells in vitro remains an alternative to the field culture of periwinkle for the production of such compounds. We previously reported that two phytohormones, cytokinin and ethylene, remarkably enhanced the accumulation of alkaloids in periwinkle cell suspensions. In this work, we investigated the effects of these hormones on the regulation of several genes of the indole alkaloid biosynthetic pathway. We show that cytokinin and/or ethylene greatly enhanced the expression of the geraniol 10-hydroxylase gene. When given together, these hormones also increased the expression of three genes belonging to the methyl-erythritol pathway. These results make it possible to consider elements of cytokinin and ethylene signalling pathways as tools for improving terpenoid indole alkaloid production through metabolic engineering.