Pulmonary involvement due to Wegener's granulomatosis (WG) can present radiologically either as diffuse infiltrates or as nodular and linear opacities. Clinical experience suggest that these radiological patterns are associated with different bronchoalveolar lavage (BAL) cell profiles, but this has not been examined formally. We compared the BAL cell profile in eight WG patients with diffuse infiltrates on chest X-ray, indicative of highly active pneumonitis, with corresponding findings in 37 patients with nodular, linear and focal low-attenuation infiltrates on high-resolution computed tomography (HRCT) which reflected low-grade, mainly interstitial disease. A control group was composed of 11 patients with pulmonary sarcoidosis. Diffuse infiltrates occurred in association with high systemic disease activity and featured a neutrophilic BAL profile in the presence of generally normal BAL lymphocytes. HRCT findings suggestive mainly of interstitial disease were associated with either a lymphocytic BAL cell profile or a normal cell pattern. Patients with a lymphocytic cell profile generally had a preferential elevation of CD4+ cells in the BAL in the presence of a normal CD4/CD8 ratio in the blood. This was a common feature of WG and pulmonary sarcoidosis. In conclusion, highly active pneumonitis and pulmonary disease of low or moderate activity in WG are associated with disparate BAL cell profiles. It remains to be examined whether the preferential elevation of CD4+ cells in the latter condition reflects a common pathogenetic role of this subset of cells in WG and pulmonary sarcoidosis.