Bovine alveolar macrophages (BAM) were harvested from nonsedated cattle, adhered to glass or plastic surfaces, and infected with parainfluenza-3 (PI-3) virus at a multiplicity of infection of 10. Control and PI-3 virus-infected BAM were compared at 24-hour intervals up to 168 hours for their ability to phagocytize antibody-coated sheep erythrocytes (EAC) and latex particles, to kill Staphylococcus epidermidis, and to alter intracellular acid phosphatase concentrations. The effect of antiviral serum on phagocytic functions of virus-infected cells was also evaluated. Compared with noninfected controls, alveolar macrophages infected with PI-3 virus were 15.3% less adherent to the glass or plastic surfaces at postinoculation hour (PIH) 72 and were 64.0% less adherent at PIH 168. Significant differences (P less than 0.05) between the numbers of control and infected BAM phagocytizing EAC were observed at PIH 24 through 72, with final values differing by approximately 50%. Similar changes were observed in the phagocytic efficiencies of individual cells. The PI-3 virus-infected BAM that were exposed to antiserum or to immunoglobulins against PI-3 virus had approximately a 2-fold greater inhibition in EAC phagocytosis than did infected BAM exposed to serum without PI-3 activity. Significant differences in latex particle phagocytosis were not observed between infected and control BAM. Compared with control BAM, the PI-3 virus-infected BAM contained significantly lower concentrations of acid phosphatase from PIH 48 through 96; at PIH 96, acid phosphatase concentrations were 4-fold less in infected than in control BAM.(ABSTRACT TRUNCATED AT 250 WORDS)