Circulating immune complexes were determined by a solid phase C1q assay in patients with divers malignancies. In Hodgkin's disease (n = 20), immune complexes were detected only in two patients during chemotherapy. Both patients succumbed shortly thereafter. In patients with testicular malignancies (n = 18), immune complexes were detected especially in patients without evidence of metastatic disease. Sequential investigations did not reveal prognostic insights. Summing up these data and the data obtained in additional patients with malignancies, it is interesting to note, that patients with carcinomas have a significant higher incidence of circulating immune complexes with malignancies of the lymphatic system. Our data, however, do not exclude presence of other than C1q binding immune complexes.