SUMMARY Nailfold capillary patterns were studied in 107 patients with Raynaud's phenomenon (RP), including patients with (n=39) and without (n=68) connective tissue disease (CTD). Capillary density was decreased in patients with sclerodactyly, digital ulcers, tuft resorption, and telangiectasia, compared with patients without these symptoms. In addition, an inverse relationship was found between the severity of RP at first presentation (as graded by photoelectric plethysmography during cooling) and the capillary density in patients with CTD (r= -0-45; p<005). In the total group of patients nailfold capillary density was inversely related to organ system involvement (r= -0-52; p<0-01). Decreased nailfold capillary density was observed, in particular, in patients with oesophageal hypomotility and in patients with chest x-rays compatible with interstitial fibrosis. As to factors supposedly involved in the pathogenesis of vascular changes in CTD, the presence of autoantibodies, increased levels of circulating immune complexes, and increased levels of acute phase reactants were all associated with a decreased number of nailfold capillaries. We conclude that loss of nailfold capillaries as observed by microscopy is a reflection of local and systemic vascular disease.