Releases ofEncarsia luteolaHoward andDelphastus pusillusLeConte were evaluated for their ability to controlBemisia argentifoliiBellows&Perring, n. sp. greenhouse-grown poinsettias. Three treatments, each replicated three times, were used to assess the impact of natural enemy releases onB. argentifoliipopulations: (1) a complete exclusion of natural enemies cage, (2) an identical exclusion cage receiving natural enemy releases as a control for cage effects, and (3) releases of natural enemies onto plants within the greenhouse but outside of either cage. Weekly releases of the parasitoidE. luteolawere initiated the week the plants entered the greenhouse and three releases ofD. pusillus, 1 wk apart, were made whenB. argentifoliipopulations rose dramatically 9 wk into the trial. Release rates for both natural enemies were one insect per plant per week. Weekly collected leaf samples were examined with the aid of a dissecting microscope. The numbers of live whiteflies were recorded by developmental stage as were the numbers of dead (resulting from natural causes,D. pusilluspredation, orE. luteolahost-feeding) and parasitized whitefly nymphs. The lack of a significant difference in whitefly densities between the two natural enemy release treatments suggested the absence of a cage effect on whitefly populations. Whitefly densities within the complete exclosure cages were significantly greater than the whitefly densities in either of the two natural enemy release treatments, indicating a significant impact of natural enemy releases onB. argentifoliiinfestations. Whitefly damage to harvested plants within the natural enemy release areas was not significantly different from the damage level observed in the grower-treated area. The direct cost associated withB. argentifoliibiological control (166.32 per greenhouse section) was ≍5 times greater than the insecticide-basedB. argentifoliimanagement program currently used by poinsettia growers. This cost differential can be reduced if the indirect environmental and worker-safety costs associated with insecticide use are included, and further reductions should accompany increased commercial availability ofD. pusillus.