The later course of IBR virus infections in 11 dairy herds in endemic areas and in an imported beef herd is described. In 2 herds the infection was limited to those animals which developed a genital infection after insemination with semen from an infected AI centre. In two other herds where genital infection was observed clinically a spreading occurred, probably because of carelessness in clinical examinations, although the possibility of an additional spreading by the respiratory route had to be considered, too. In one herd signs of a respiratory disorder were noticed and assumed to have been caused directly by IBR virus. In the other 7 herds a spreading by the respiratory route was evidenced serologically. In some of these herds there were no indications of spreading after the extensive initial spreading, while in others there were single cases of infection later on, in particular in one small herd where the ventilation was inadequate.