The influence of insulin and 2-deoxy-glucose (d-glucose) on the intracellular protozoan Toxoplasma gondii replication in 3T3-L1 cells was investigated. Insulin and d-glucose had a dose-responsive mitogenic effect on intracellular T. gondii replication and development in 3T3-L1 cells. Insulin concentrations between 10−2 and 10−1 μg/ml combination of 4.5 g/l d-glucose in DMEM medium gave maximum stimulus to T. gondii replication. The number of tachyzoites increased rapidly, with the growth peaking typically on day 3 or 4 of culture, and then declining quickly. However, insulin, in the absence of d-glucose, had comparably less effect on T. gondii growth than two of their combination. d-glucose concentrations significantly affected the tachyzoite replication and appear to be indispensable for maintaining the host 3T3-L1 cells.