In order to asses the effect of pseudorabies virus (PRV) infection on the function of swine alveolar macrophages (AM), lung lavage cells were cultured, infected with one of six strains of PRV, and various activities were measured. Activity measurement included viability, phagocytosis of yeast, phagosome-lysosome fusion, phagocytosis of opsonized particles, and superoxide release. AM were infected with 5 x 10-3 PFU/cell, and the comparative assessment of functions was performed at 18-20 h postinfection. Cell viability in PRV-infected cultures ranged from 79 to 94% of the viability in noninfected cultures. Phagocytosis of yeast was significantly reduced only in the AM cultures infected with the strain S-62. Phagosome-lysosome fusion was depressed in cultures infected with the strains S-62, 4892, 3816, and BUK. The phagocytosis of opsonized sheep red blood cells showed significant differences between noninfected and PRV-infected cultures in all cases except cultures infected with the strain PRV-C. The O2 release after stimulation with opsonized zymosan was significantly reduced in all the PRV-infected cultures. The effect of PRV infection on AM functions that are related to the bacterial activity of such cells suggests that PRV-induced AM dysfunction might have a role in the increased susceptibility of PRV-infected pigs to bacterial pneumonia.