Histopathological criteria were used to classify twenty-four patients with chronic urticaria into three groups, which were then studied to establish whether circulating immune complexes (CICs), complement activation and deposition of immunoreactants are confined to patients with urticarial vasculitis. Group I (three patients) had classical urticarial vasculitis, and two of these patients showed hypocomplementaemia with evidence of C3 conversion and deposition of immunoreactants in lesional and uninvolved skin. Ten patients (group 2) with a dense perivascular mixed-cellular infiltrate had normal or raised complement levels and infrequent evidence of C3 conversion. Immunoreactants were detected only in their lesional skin. Eleven patients (group 3) had only a sparse perivascular infiltrate. In this group, complement was normal and immunofluorescence was essentially negative. Cryoglobulins were detected in group I patients only. Monoclonal rheumatoid factor and C1q binding were positive in all group I patients, half the group 2 patients and none of the group 3 patients. This study suggests that urticaria and urticarial vasculitis form a disease continuum, and identifies a group of patients with features intermediate between urticarial vasculitis and ordinary urticaria.