OBJECTIVES Interstitial lung disease (ILD) is a key prognostic factor in connective tissue disorders (CTDs). The aim of our study was to assess the changes in pulmonary functional tests (PFTs) in various CTDs, including anti-synthetase syndrome (SYN), systemic sclerosis (SSc) and mixed connective tissue disorder (MCTD), following the use of rituximab therapy. METHODS A multicentre retrospective analysis of patients with ILD secondary to SYN (n=15), MCTD (n=6) and SSc (n=23). PFTs were performed at baseline and at 1 and 2 years of follow-up. The primary outcome was the change in forced vital capacity (FVC) at 1 year. RESULTS In the SYN population, median FVC changed from 53.0% (42.0-90.0) at baseline to 51.4% (45.6-85.0) at 1 year and 63.0 (50-88) (p=0.6) at 2 years (p=0.14). In SSc, FVC changed from 81.0% (66.0-104.0) at baseline to 89.0% (65.0-113.0) at 1 year (p=0.1) and 74.5 (50-91) at 2 years (p=0.07). In the MCTD population, FVC changed from 64.5% (63.0-68.0) at baseline to 63.0% (59.0-71.0) at 1 year (p=0.6) and 61 (59-71) after 2 years (p=0.8). DLCO showed a trend for improvement in the SYN population (p=0.06 at 1 year and 0.2 at years) while changes remain non-significant in the SSc and MCTD patients. In SYN patients, the percentage of responders at 1 year for FVC (33.3%) was greater than in SSc (9.5%) (p=0.07) and MCTD (17%) (p=0.45). RTX showed a satisfactory safety profile. CONCLUSIONS A trend of improvement of PFTs was observed in SYN patients although not reaching significance, while SSc and MCTD patients were stabilised.