Ten patients with pulmonary hypertension associated with diffuse systemic sclerosis (1 patient), the CREST syndrome (calcinosis cutis, Reynaud's phenomenon, esophageal dysmotility, sclerodactyl, telangiectasia) (6 patients) and mixed connective tissue disease (3 patients) were studied to assess the effect of oral nifedipine on pulmonary and systemic hemodynamics. Each patient underwent right-sided cardiac catheterization just before nifedipine administration. Thereafter, oral nifedipine was administered in 10 mg increments every 90 minutes until pulmonary vascular resistance normalized or a total dose of 30 mg was achieved. Hemodynamic measurements were obtained at 30-minute intervals for 3 hours, then hourly for 9 hours (acute study). Hemodynamic studies were repeated 3 to 6 months after the initial catheterization with the minimum dose of oral nifedipine (administered every 8 hours) required to achieve maximal reduction of pulmonary vascular resistance in the acute study (long-term study). In the acute study, oral nifedipine produced a significant decrease in mean pulmonary vascular resistance from 6.3 +/- 3.8 to 4.3 +/- 3.6 U (p less than 0.001). Similar changes in pulmonary vascular resistance were noted in the long-term study (n = 6). The results indicate that oral nifedipine is capable of producing an acute and sustained reduction in pulmonary vascular resistance in patients with pulmonary hypertension associated with diffuse systemic sclerosis, the CREST syndrome and mixed connective tissue disease.