Macrophages play a crucial role in respiratory viral infections. However, the mechanisms by which these cells are recruited locally are not fully understood. The current authors studied the role of the chemokines monocyte chemotactic protein (MCP)-1, -2, -3 and -4 on monocyte/macrophage recruitment during respiratory viral infections. Levels of these chemokines were investigated in nasal aspirates from 6-12-yr-old children suffering from respiratory viral infections, caused by rhinoviruses, influenza viruses, parainfluenza viruses, adenoviruses and respiratory syncytial virus. MCP-3 and -4 were significantly higher in samples derived from virus-infected children compared with samples from the same children when they had been asymptomatic. Concentrations of both chemokines were found to significantly correlate with the number of recruited nasal macrophages. Chemotaxis assays showed that purified MCP-3 and -4 from nasal aspirates showed biological activity in vitro. There were no significant differences in MCP-1 and -2 levels between both groups. The present data indicates that monocyte chemotactic protein-3 and -4 may have an important role in macrophage recruitment in children with proven upper respiratory viral infections. These chemokines could be potential targets for therapeutic intervention in respiratory viral infections.