This study aimed at determining presence of CYP 450 variant alleles (CYP2C8*2, CYP2C8*3, CYP2B6*6, CYP3A4*1B and CYP3A5*3) responsible for the metabolism of artemisinin-based combinations employed in the treatment of uncomplicated malaria and complicated malaria (injectable artesunate) in Tanzania where malaria is endemic. The gene discussed is CYP3A4; the disease is malaria.