Biological efficacy of three insecticides of natural origin (azadirachtin, strain ATCC 74040 of entomopathogenic fungus Beauveria bassiana, and spinosad) and of one synthetic insecticide (acetamiprid) in the control of larvae and adults of whitefly (Trialeurodes vaporariorum) was investigated. The trial was set in a commercial greenhouse at the Debrc locality (N44 degrees 37.556'; E019 degrees 57.012') on tomato plants. Products based on azadirachtin and B. bassiana were applied twice at four-day interval. The trial was conducted in four replicates in a randomized block design. The efficacy was assessed 7, 14 and 21 days after treatment. Azadirachtin (product Neem-Azal T/S, 0.5% and 1%) achieved the efficacy of 55.4-67% (lower rate) and 68.1-87% (higher rate) in adult control, while the efficacy in larval control was 71.9-91.3% i.e., 67.1-92.2%. Efficacy of B. bassiana (product Naturalis, 0.1% and 0.2%) in adult control was 63.2-81.7% (lower rate) and 62.7-87.1% (higher rate), while in the control of larvae the efficacy of 73.2-87.7% i.e., 82.6-94.6% was recorded. Efficacy of spinosad (product Laser 240-SC, 0.05%) was 72-81.5% (adults) and 47.176.9% (larvae). Acetamiprid (product Mospilan 20-SP, 0.025%) achieved efficacy of 80.4-84.8% (adults) and 40-62.3% (larvae). The results obtained indicate that the investigated natural insecticides are potentially good alternative to synthetic insecticides in the control of whitefly adults and larvae on tomato grown in greenhouses.