Assays for immune complexes are best directed toward an analysis of the immune complexes or their deposition in various human disease tissues. In most cases, the best approach is to receive freshly biopsied nonfrozen material that is then snap frozen and sections cut and stained to test for the presence of appropriate antigen or antibody. In some cases, the antigen is still intact after formalin fixation and parafin blocks are prepared. But in these specimens, one always runs the risk of destroying the appropriate antigen or antibody during the fixation process. Examples of the diseases studied in this manner are renal immune complex disease such as seen in SLE, acute poststreptococcal glomerulonephritis, or psoriasis.