The aim of this study was to compare the efficacy of intravenous cyclophosphamide (IVCYC) versus oral enalapril in mild or moderate pulmonary hypertension (PH) in systemic lupus erythematosus (SLE). Thirty-four patients with SLE who had systolic pulmonary artery pressure (SPAP) > 30 mmHg by Doppler echocardiography were randomized to receive IVCYC (0.5 g/mt2 body surface area, monthly), or oral enalapril (10 mg/day) for six months. The primary outcome was the significant decrease in SPAP. An additional outcome measure included the improvement in the heart functional class (NYHA). Sixteen patients received cyclophosphamide and 18 enalapril. IVCYC decreased the median values of SPAP from 41 to 28 mmHg (P < 0.001), and enalapril from 35 to 27 mmHg (P = 0.02). IVCYC reduced more than twice as much SPAP than enalapril (P = 0.04). In those patients with SPAP > or = 35 mmHg, cyclophosphamide decreased from 43 to 27 mmHg (P = 0.003), but enalapril was not effective (P = 0.14). The NYHA functional class improved only in those with cyclophosphamide (P = 0.021). Also IVCYC had a higher frequency of side effects including infections (RR = 1.6; 95% CI, 1.001-2.47), and gastrointestinal side effects (RR = 14.6; 95% CI, 2.15-99.68). We concluded that IVCYC was effective in mild and moderate PH associated with SLE. Further research is needed to evaluate its long-term efficacy.