Sera from 21 patients with mesangiocapillary glomerulonephritis were examined for the presence of cryoglobulins, for the complement levels and in 8 cases for the C3 splitting activity. Patients were divided, on the basis of histology, into two groups; the first of 10 patients with subendothelial deposits, the second of 11 patients with intramembranous dense deposits. The incidence of cryoglobulins and the cryoprecipitate components were similar in the two groups. As previously described, in the first group low levels the C3 was low without alterations in the C4 levels. There are no previous reports on this high incidence of cryoglobulins in dense deposits disease and these data add further support to the hypothesis that this disease is, at least partially immunecomplexes mediated.