The resistance of Dermanyssus gallinae , the red poultry mite, to a pyrethroid acaricide, permethrin, and to an organophosphate, dichlorvos, was examined on five French poultry farms which had experienced problems in controlling mite populations and on one farm with no problems. The concentration of permethrin requlired to kill 50 per cent of the mites on the five farms was between eight and 40 times the concentration required on the control farm. In contrast, no resistance to dichlorvos was detected. This is the first description of resistance to a pyrethroid in D gallinae in France.