Industrial production of valuable secondary metabolites by plant cell cultures is generally hampered by low productivity. This productivity is controlled by several factors, one of these is temperature. Secondary metabolites are in most cases produced in a two-stage process: biomass growth, followed by secondary metabolite production. In part I of this study the optimal temperature for biomass growth was investigated aiming at: maximal formation of biosynthetic active biomass, minimal formation of useless by-products, These processes each had their characteristic temperature dependence. The growth of Catharanthus roseus biomass for the production of ajmalicine was found to be optimal at 27.5degreesC. The effects of oxygen limitation are discussed. In part II the temperature effect on ajmalicine production was investigated. The productivity was governed by two processes: induction and production. Induction and production were both optimal at 27.5degreesC. The length of the induction period was easily estimated from a rapid concentration decrease of the precursor tryptamine.