The western flower thrips, Frankliniella occidentalis (Pergande), is one of the most important insect pests in the Mediterranean region of Turkey. Thrips infestation is the main cause of vegetable crops losses in low polythene tunnels and plastic greenhouses. Chemical control has been the primary means to control F. occidentalis in protected cultivation systems in Turkey. A search of alternatives to conventional insecticides for the control of F. occidentalis has drawn increased interest in the use of biocontrol agents. This study evaluated the control efficiency of F. occidentalis on eggplants through releases of the predatory mite Amblyseius swirskii (Athias-Henriot) at a rate of 50 adults per m(2) in plastic greenhouses or low polythene tunnels. Samplings of F. occidentalis from flowering to harvesting of the eggplants revealed that neither preventative nor curative releases of the predatory mite reduced the thrips population densities below a mean of 3 thrips per flower (i.e. control threshold). We discuss various factors that may have affected the efficiency of the predatory mite on eggplants or the failure of the biological control.