Gametocytogenesis induction medium (RPMI-FSC reactive medium), prepared with a mixture of the culture supernatant from anti-Plasmodium falciparum antibody-producing hybridoma cells and hybridoma cell lysate, consistently induced gametocytogenesis in culturedP. falciparum. Gametocytogenesis was induced in three strains (0662, FCB 1, and FCR-3) and one clone (R·FCR-3) as has previously been described in two other strains (Ono et al. 1986). Both caffeine (2 mM/ml) and calmodulin (5 μg/ml) enhanced the effects of RPMI-FSC reactive medium. Furthermore, gametocytes that appeared after treatment with RPMI-FSC reactive medium continued their development to ookinete formation in candle jar culture with Waymouth's medium.