The authors review the role, clinico-serological correlations and the putative pathogenetic relevance of a number of immunological parameters in essential mixed cryoglobulinemia. On the whole, in spite of the fact that levels of cryoglobulins, immune complexes, complement as well as reticuloendothelial splenic function are frequently abnormal in this condition, they are generally poorly correlated with clinical features. Therefore, it is postulated that this apparent discrepancy may either be due to the contemporary presence in the same serum of many types of immune complexes with different toxicity, or to the influence of rheumatoid factor on the nature of circulating immune complexes.