Sera from 683 pigs of 41 swine herds with clinical atrophic rhinitis (AR), from 477 pigs of 37 herds with no AR history, from 267 breeding sows and breeding boars for slaughtering, from 22 boars at an artificial insemination centre, and from 103 SPF pigs were tested for the presence of antibodies to porcine cytomegalo virus (PCMV). The herds examined were spread all over the Netherlands. For the presence of antibodies to PCMV the indirect fluorescence antibody test was used. To obtain the antigen, the PCMV had been grown in pig lung macrophage cultures in Petri dishes for 10--12 days. These macrophages were dropped into the wells of slides. The serum dilution 1:20 of all the 103 sera from SPF pigs were negative, but 93 per cent of the other sera were positive. No marked differences were found between swine herds with clinical atrophic rhinitis and herds with no AR history. The FA titres in both types of herds seem to be at a comparable level.