The leukocyte adhesion glycoprotein complex CD11/CD18 has been shown to be important in mediating neutrophil accumulation at sites of inflammation in many experimental models. The exception is the lung, where neutrophil accumulation into the airspaces can be CD18-dependent and -independent, according to the stimulus used to induce pulmonary inflammation. By using the anti-CD18 mAb 60.3, this study examined the role of CD18 on neutrophil accumulation in the lungs of rabbits induced by a local intrabronchial instillation of C5a or interleukin-1 alpha (IL-1 alpha) into the upper lung lobes. For comparison, cutaneous inflammation was induced in the same animals by intradermal injection of the same mediators. Pretreating rabbits with 60.3 abolished accumulation of 111In-labeled neutrophils in skin induced by both C5a and IL-1 alpha. In contrast, in the same animals, C5a-induced accumulation of neutrophils in the lung was not significantly affected by 60.3, while neutrophil accumulation in response to IL-1 alpha showed a significant, but not absolute, dependency on CD18. External gamma scintigraphy of 111In-labeled neutrophils demonstrated that the kinetics of cell retention in the lung was similar for both C5a and IL-1 alpha. In summary, accumulation of neutrophils to sites of inflammation in cutaneous inflammation shows an absolute dependency on CD18, while migration of these cells to sites of inflammation in the lung can be largely independent of this adhesion molecule. These data indicate that the mechanisms responsible for accumulation of neutrophils in cutaneous and pulmonary inflammation are different.