Larvivorous copepods (Macrocyclops, Mesocyclops and Acanthocyclops) were tested for their sensitivities to commonly used mosquito larvicides and adulticides. The cyclopoids were not harmed by Bacillus thuringiensis (H-14) (B.t.i.) or larviciding oil. Control of mosquito larvae in field trials was accelerated by applying B.t.i. at the same time cyclopoids were introduced to a breeding site. Among adulticides tested, the cyclopoids were least sensitive to permethrin. Field trials demonstrated that permethrin does not harm cyclopoids when applied at label specifications.