Rheumatoid nodules are especially found in patients with seropositive rheumatoid arthritis (RA). It is often suggested that the genesis of these lesions is due to a vasculitis in smaller capillary vessels or venules. To test this hypothesis we studied fresh nodules in 13 patients, all with classical or definite RA. In 7 cases a total of 8 nodules were removed within 10 days of origin and in 6 other cases between 2 and 8 weeks. In the former group immunofluorescence was found in 5 out of 8 cases, and in the latter group 3 out of 6 were positive. Immunoglobulin deposition together with complement was found only in cases of 10 days' duration or less. No correlation was found with the patient's age or disease duration, ESR, ANA positively, Rose titre, haemoglobulin, or use of prednisolone. In 3 out of 7 nodules younger than 7 days no palisade layer was found, whereas in older nodules this layer was always present. Vasculitis was not more frequently present in the cases with younger nodules. Our study does not support the hypothesis that vasculitis is the primary cause of nodules.