The host range ofTetranychus lintearius was examined experimentally to determine if the mite could be safely introduced into New Zealand for the biological control of gorse,Ulex europaeus (Leguminosae: Genisteae). The rationale for choosing test plants was the same as that employed for testing insect species as biological control agents. Outdoors, mite colonies could be transferred successfully from gorse plant to gorse plant, but could not re-establish on any of 39 other plant species progeny to develop, was measured on 58 plant species other than gorse. Apart fromUlex europaeus andU. minor, development was completed only onPhaseolus vulgaris andGlycine max. Further experiments using 22 bean cultivars showed that mites could not complete a second generation on detached leaf cultures, could not form permanent colonies on potted plants in the glasshouse, and remanned only a short time when transferred to bean plants in the field. Tetranychus lintearius has never been recorded from any plant butUlex species. This fact, coupled with the results of host-range testing, suggests that the mite is sufficiently host-specific to be safely used as a biological control agent for gorse in New Zealand.