In a previous study we induced digital vasospasm with cold pressor stimulus, and an acute decrease in the lung diffusing capacity for carbon monoxide (Dsb) resulted. We hypothesized its cause to be spasm occurring simultaneously in the pulmonary vasculature and the digital arteries. We measured in this study the Dsb, the diffusing capacity of the pulmonary membrane (Dm), and the volume of blood in the pulmonary capillaries (Vc) after cold-induced digital vasospasm in patients with Raynaud's phenomenon. Control subjects showed no significant decrease in Dsb, Dm, or Vc after cold exposure. Eight of 12 subjects with Raynaud's phenomenon had a significant decrease in Dsb 60 min after testing (25.3 +/- 6.6 vs 19.8 +/- 6.1 ml/min/mm Hg, p less than 0.01). The acute decrease in Dsb was due to a significant decrease in Vc (54 +/- 20 vs 39 +/- 10 ml, p less than 0.05), while Dm was unchanged (52 +/- 17 vs 51 +/- 20 ml/min). Four subjects who had a decrease in Dsb after cold challenge had repeated studies later after pretreatment with sublingual nifedipine. The magnitude of change in Dsb was similar to that observed in the untreated state (23.6 +/- 10.6 vs 20.9 +/- 9.6 ml/min/mm Hg). We conclude that digital vasospasm is accompanied by an acute reduction in Vc in both primary and secondary Raynaud's phenomenon and indicates concurrent vasoconstriction within the pulmonary vaculature.