The purpose of this study was to determine the ability of technetium-99m J001X scintigraphy to image active pulmonary involvement in patients suffering from rheumatoid arthritis (RA). J001X is a fully characterized acylated poly(1,3)galactoside, isolated from Klebsiella membranes, which is able to bind recruited macrophages after aerosol administration. J001X scintigraphy was compared with high-resolution computed tomography (HRCT), pulmonary function tests (PFTs) and bronchoalveolar lavage (BAL) in 15 patients suffering from RA. Patients were considered to have pulmonary involvement when they had an interstitial syndrome on HRCT and a decrease of 20% in TCO/VE (transfer coefficient) on PFTs and/or an abnormal BAL (lymphocytosis higher than 20% and/or percentage of neutrophils higher than 10%). Pulmonary involvement was present in eight patients, and absent in seven. Of the eight patients with pulmonary involvement, all had abnormal BAL, two had an interstitial syndrome on HRCT, two had decreased TCO/VE and three had positive J001X scintigraphy. Of the seven patients without pulmonary involvement, six had normal BAL (not available in one), two had an interstitial syndrome on HRCT, one had decreased TCO/VE and two had positive J001X scintigraphy. According to our gold standard of pulmonary involvement, the sensitivity of J001X scintigraphy for the detection of pulmonary involvement in RA was 37.5%, the specificity was 71.4% and the positive predictive value was 60%. The ability of J001X scintigraphy to detect active pulmonary involvement during RA appears unclear in this study but it may detect processes unnoticed by the other modalities. These patients will be followed 12 and 24 months later and the changes in J001X scintigraphy, HRCT and PFTs will be compared to demonstrate whether J001X scintigraphy is able to assess an active process in the pulmonary involvement during RA and to specify its predictive value.