Forty-two patients presenting with Raynaud's phenomenon (RP) were prospectively evaluated for pulmonary function changes over a 6-year followup period. Fifteen patients had secondary RP at presentation, 27 patients had nonsecondary RP. In the latter group, decreased pulmonary diffusing capacity (Tlco) was observed in only 2 patients (7%) whereas 9 patients with secondary RP (60%) had decreased Tlco. In the group of patients with nonsecondary RP exhibiting one or more autoantibodies, Tlco values were lower than in the group without autoantibodies (p less than 0.01). In patients with nonsecondary RP the duration of disease was correlated with the level of Tlco (r = 0.55), probably explained by a higher prevalence of truly primary RP in patients with longstanding nonsecondary RP. During followup no significant changes in pulmonary function were observed in the group with nonsecondary RP. We conclude that pulmonary function testing in patients presenting with nonsecondary RP without autoantibodies does not appear of clinical value.