The leaves of Catharanthus roseus (L.) G. Don. are a valuable source of the terpenoid indole alkaloid (TIA) anticancer drugs, vinblastine and vincristine. In particular, the precursor molecules vindoline and catharanthine are harvested from leaves and used for the semisynthetic production of vinblastine and vincristine. Because of this application, catharanthine and vindoline can be used to screen for high-yielding TIA cultivars. In this study, we compared the TIA concentrations in the leaves of 64 different cultivars of C. roseus in the soil experiments. The highest concentration of serpentine was found in Cooler Rose Hot (461 +/- 46 mu g/g DW). Concentrations of vindoline (2082 +/- 113 mu g/g DW) and catharanthine (2903 +/- 384 mu g/g DW) were highest in Pacifica Peach. To eliminate the abiotic and biotic effects of the soils on the plant growth, sterile agar experiments were performed to investigate the TIA concentrations and mRNA transcript levels of selected TIA pathway genes. Six cultivars were investigated (two each of the high level, mid level, and low level producers of TIAs). (C) 2011 American Institute of Chemical Engineers Biotechnol. Prog., 27: 937-943, 2011