Phytoseiulus persimilisAthias-Henriot was introduced on hop plants at 10, 20, and 30 per plant for control of the twospotted spider mite,Tetranychus urticaeKoch.P. persimilisbecame established on hops but the predator-prey populations were retarded by an infestation of the hop aphid,Phorodon humuli(Schrank). Phosalone when applied to reduce aphid numbers also killedP. persimilisbut permitted survival ofTyphlodromus occidentalisNesbitt, a native phytoseiid predator ofT. urticaeon hops. A laboratory study of the interaction ofP. persimiliswithT. occidentalisand the coccinellidsStethorus punctillumWeise and the convergent lady beetle,Hippodamia convergensGuérin-Meneville, indicated thatT. occidentalisandS. punctillumfed on eggs and larvae ofP. persimilis.H. convergensfed on all stages ofP. persimilis. In the field,T. occidentalisfed onP. persimiliseggs and larvae.P. persimilisdid not feed onT. occidentaliseggs or larvae.T. occidentalisappears to be a better candidate thanP. persimilisfor control ofT. urticaeon hops.