The aim of the experiment was to check the effectiveness of the varroacide veterinary product called PolyVar Yellow® (flumethrin 275 mg) in field conditions in the area of north-eastern Poland. The experiment was carried out on twenty bee colonies, of which in ten (group PY) were tested with the veterinary product and the remaining ten constituted a control group without anti-varroosis treatment (group C). Treatment began in mid-August and lasted until the end of October when bee flights ceased. A control treatment was then conducted with a 3.2% oxalic acid solution. The effectiveness of Varroacide of PolyVar Yellow® was estimated on the basis of the parasite falls on the