The effect of initial K(L)a on the batch culture of Catharanthus roseus ID1 in a 12.5-L bioreactor has been examined. Optimum K(L)a values were found for both growth and alkaloid accumulation. Different sparger designs were used to alter the K(L)a values. High K(L)a values caused increased aggregation of the cultures, depressed biomass yields, and altered patterns of alkaloid accumulation.