The functional response for various stages of the predatory mite,Amblyseius cucumeris(Oudemans), on first instars of western flower thrips,Frankliniella occidentalis(Pergande), was determined. The predation trials were conducted on greenhouse cucumber and sweet-pepper leaf disks over a 24-h period at 26 ± 1°C and 12:12 (L:D) photoperiod. Prey densities ranged from 1 to 40 larvae per leaf disk. The mated female adults ofA. cucumeriswere the most effective predatory stage, whereas all male stages were ineffective predators. Use of this information on the predator-prey relationship betweenA. cucumerisandF. occidentalisfor improving and predicting the outcome of biological control ofF. occidentalison greenhouse crops is discussed.