Stock of A/duck/Tuva/01/06 was produced in 9 days-old chicken embryos. Allantoic fluid was aliquoted and stored at -80°C. The infectivity of stock viruses was determined in 10 days-old embryonated chicken eggs; titers were calculated by the method of Reed and Muench [10] and were expressed as log 10 of 50% egg infective dose (EID 50 ) in 1 ml of allantoic fluid.