Immune Complexes and Human Cancer, the fifteenth volume of Contem porary Topics in Immunobiology, is a compilation of information derived from recent studies on the role of circulating immune complexes (CIC) in the patho genic manifestations of a variety of human cancers. Technical improvements in the detection of CIC in body fluids have resulted in data that indicate that CIC do occur in different types of cancer. In addition, tumor-associated antigens and antibodies have been detected in immune complexes of cancer patients’ sera. Until recently the exact role and clinical relevance of immune complexes have been the subject of debate, partially because of the problems encountered in measuring immune complexes. But these problems are being confronted as more accurate measurement protocols are developed. Technical refinements, along with strict protocols, have provided evidence of heterogeneity in CIC, a factor that makes accurate detection of immune complexes in cancer patients difficult. Recent insights indicate that the measurement of immune complexes in cancer patients may be clinically useful not only as a tumor marker, but also in regard to the deranged immune response of tumor-bearing hosts and other disorders such as nephrotic syndrome, immune anemias, and clotting dysfunction.