Objectives Farmers who treat their sheep for ectoparasites with organophosphate (OP) dips report a range of flu-like symptoms known as 'dipper's flu'. The nature and causes of 'dipper's flu'are poorly understood. The aim of this study was to investigate whether OP exposure was associated with acute ill health. Methods Data on the daily incidence of general illness, tiredness, headaches, fever, muscle aches, runny nose, sore throat, coughing, nausea and eye irritation (symptom complexes) and sheep treatment practices during the wee