Bronchoalveolar lavage (BAL) was carried out in 30 patients of idiopathic pulmonary fibrosis (IPF), 10 patients of sarcoidosis and 10 normal subjects who served as controls. The total cell counts were higher both in the IPF (24.8 x 10(5)/ml) and sarcoidosis (19.3 x 10(5)/ml) as compared to the normal controls (9.8 x 10(5)/ml). The difference was statistically significant in both the groups (p less than 0.001 and less than 0.05 respectively). Patients with IPF showed a predominant polymorphonuclear response although the lymphocytes were also increased whereas patients of sarcoidosis had a lymphocytic response in the BAL fluid. In 6 patients with IPF the study was repeated after 6 weeks of steroid therapy and a decrease in the total cell count and polymorphonuclear cells (%) was noted.