Six to nine horses per month (total of 94 in a year) were examined for stomach worms in the Settat region of Morocco. All the animals were infected by at least one helminth species. Habronema muscae occurred in 95–8%, H. majits in 75.6% and Trichostrongylus axeiin 80.9% of horses. Polyparasitism was observed in 93.6% of horses. Both for Habronema spp. and T. axei the peak worm burden was observed in November and minimum in June. The infection pattern Habronema spp. was directly related to the period of activity of fly vectors.