Collagenase, collagenolytic activity and tissue inhibitor of metalloproteinases were evaluated in bronchoalveolar lavage from 25 patients with hypersensitivity pneumonitis and four control subjects. Patients were followed between two and three years, after which they were classified as "healed," "improved," or "worsened." In control samples, immunoreactive collagenase was not detected. The enzyme was present in four of seven patients who healed, six of ten patients who improved, and four of eight patients who worsened. There was no relationship between the presence or absence of BAL collagenase or its concentration and the evolution of the disease. Latent collagenolytic activity was detected only in 5 of the 14 patients who displayed immunoreactive collagenase. Regarding collagenase inhibitor, TIMP was present in BAL fluid from all patients and normal subjects. Although the highest values were found in two cases who healed or improved, there was not a statistically significant difference among the three groups of patients, neither between patients nor control subjects. These findings suggest that at least in HP, the presence of collagenase, collagenolytic activity, or TIMP in BAL fluid is not associated with the prognosis of the disease.