Bronchoalveolar lavage (BAL) and histology of transbronchial forceps biopsy was performed in 59 patients with rheumatoid arthritis (RA) to evaluate the in vivo effects of disease modifying drugs (DMARD). All patients had no clinical pulmonary symptoms and there was no evidence of drug induced alveolitis. Patients were divided into 5 subgroups according to drug treatment: 9 patients taking chloroquine, 15 patients gold, 8 patients penicillamine, 8 patients methotrexate (MTX) and 19 patients not taking DMARD. Duration of DMARD regimen was more than 3 months. No patient was treated with corticosteroids. BAL results revealed an increased percentage of lymphocytes and a diminished proportion of alveolar macrophages in patients treated with gold, penicillamine, MTX and no DMARD. In contrast, patients receiving chloroquine had a normal distribution of lymphocytes and macrophages as seen in a control group of 15 persons. Patients taking MTX showed a normal distribution of T and B lymphocytes and DR positive cells, whereas patients receiving chloroquine, gold, or penicillamine had an elevated proportion of T lymphocytes and DR positive cells and a diminished percentage of B lymphocytes. The latter was also observed in patients not taking DMARD. The percentage of natural killer cells was significantly elevated only in the penicillamine group. Patients receiving gold had higher absolute values of CD3, CD4 and DR positive cells. Abnormal lung histology was associated with an increased percentage of lymphocytes and with higher DR positive cells in BAL. Patients not receiving DMARD had a significantly higher percentage (42.1%) of abnormal histologic features of lung tissue than patients receiving DMARD (17.5%).(ABSTRACT TRUNCATED AT 250 WORDS)