The effect of a regular anthelmintic treatment during the grazing period on milk production and milk composition was measured in a dairy goat farm. One month before turnout, 92 goats were given 10 mg.kg-1 febantel and then allocated to 2 equivalent groups according to their levels of milk production. The first group was given febantel monthly, the second group was kept as an untreated control. Parasitological, haematological and serological data were collected monthly from March to September. Milk production data were recorded from March to August, goats being dried up in September. Results of strongyle egg counts, serum inorganic phosphate concentrations and 4 necroscopic examinations indicated a low level of nematode infection composed almost exclusively with Trichostrongylus colubriformis in untreated goats. No significant changes in milk yield, fat and protein content were detected between treated and untreated groups. Moreover, the impact of monthly anthelmintic treatment on milk production was different depending on the initial level of milk yield. Anthelmintic treatment induced a 4-8% increase in milk production for goats with the highest milk yield at the start of the experiment, whereas no beneficial effects were recorded for goats with the lowest milk yield.