Catharanthine production in Catharanthus roseus suspension cell cultures was increased by about 4-fold to 28 mg l(-1), 23 mg l(-1) and 24 mg l(-1) by adding sodium alginate, mannitol or polyvinyl pyrrolidone, respectively. Sodium alginate and polyvinyl pyrrolidone also enhanced ajmalicine production to 28 mg l(-1) and 31 mg l(-1), respectively. Up to 55-70% of the total alkaloids were released into the medium. These treatments could stimulate higher alkaloid production in C. roseus cell cultures than NaCl and KCl stresses. The possible mechanisms for these treatment effects are discussed.