Trials were set up to ascertain whether the observed occurrence of streptothricosis lesions at dorsal sites on cattle in Antigua was related to the feeding activity of flies. Animals in two herds were treated with insecticide while a third herd served as an untreated control group. There was no significant difference in the occurrence or distribution of lesions on animals in all the three herds over a two month observation period except that a higher proportion of animals in one of the treated herds was affected at the end of the study.