EDITOR,--Recent anecdotal reports and one clinical study have suggested that head lice found in parts of Israel and France have acquired resistance to the pyrethroid insecticides permethrin and phenothrin.*RF 1, 2, 3* In Britain most failures of treatment reported to us have been attributable to causes other than resistance, including shorter than expected residual protection after treatment with permethrin. When working in north London in January 1994 we obtained lice and hair samples from children whose families had obtained pyrethroid products from more than one country and used them …