The purpose of this study was to determine if pseudorabies virus (PrV) interfered with normal alveolar macrophage phagocytic functions. Porcine alveolar macrophages (PAM) obtained by pulmonary lavage were exposed to PrV. At 1 hour postinfection, cells were challenged with Pasteurella multocida labeled with 3[H] thymidine. The phagocytosis assay was performed by measuring total radioactivity 1 hour after Pm challenge in a soft-beta spectrophotometer. Intracellular killing was measured by counting viable bacteria 3 hours after P. multocida challenge. Phagocytic values of PrV-infected and control PAM ranged from 11% to 20%, a non-significant difference. Values for intracellular killing for PrV-infected PAM ranged from 7.1 X 10(5) to 1 X 10(6) in contrast to 5.1 X 10(1) to 1.8 X 10(2) for the control PAM. This difference in killing function was significantly lower in PrV-infected PAM than in control cells (P less than 0.01). This alteration of macrophage function may be a factor in the pathogenesis of PrV-Pm mediated pneumonia in pigs.