Five different tissue cultures of Catharanthus roseus were investigated for the indole alkaloids serpentine and ajmalicine. In al1 ce11 lines serpentine could be detected, whereas ajmalicine was only present sometimes at low concentrations. The serpentine content of the different ce11 lines differed under the same cultural conditions, thus indicating that it was regulated by genetic factors. In one ceIl line the serpentine content could be regulated by cultural conditions from 0,01 to O,SO/o on a dry weight basis. This means that serpentine occurs in tissue cultures in amounts comparable with those found in roots of Catharanthus which serve as source for the technical production of serpentine.