Phagocytosed immune complexes in polymorphonuclear (PMN) leucocytes of sixty-nine patients with Raynaud's phenomenon were studied by scoring the cells for IgG and complement inclusions. The results were compared with the degree of vasospasm, as measured by photoelectric plethysmography of the fingers after cooling. Median IgG and complement scores of PMN cells were significantly elevated in patients with Raynaud's phenomenon when compared with those of the control group (P less than 0.01). Patients with a positive (n = 35) or a strongly positive (n = 11) plethysmographic test showed significantly higher median IgG and complement scores than those with a negative plethysmorgraphic test (n = 23). They also showed elevated IgG and complement scores in a greater proportion (89 and 100%, respectively, vs 48%).Thus, a positive relationship was shown to exist between the degree of vasospasm and the levels of phagocytosed immune complexes in circulating PMN leucocytes. In secondary Raynaud's phenomenon high levels of phagocytosed immune complexes were found. In primary Raynaud's, patients with some clinical or laboratory signs of an auto-immune disease (n = 12), who were classified as "suspected secondary", had higher IgG and complement scores than those without such signs (n = 37). This suggests that the test for immune complex detection may distinguish patients with connective tissue disease-associated Raynaud's phenomenon from those with truly primary Raynaud's, in an early stage of the disease. The clinical and patho-physiological implications of these findings with regard to the Raynaud phenomenon are discussed.