In order to assess the relationships of erythrocyte sedimentation rates (ESR) and various acute phase reactants in diagnosing and following the remissions and exacerbations of various chronic diseases, multiple tests were performed on patients for whom an ESR was ordered. The Wintrobe and Westergren ESR, plasma and serum viscosity, hemoglobin, blood cell indices, fibrinogen, serum protein electrophoresis, triglycerides, and complement (C-3) were performed. A discussion of the relative merits of correcting the Wintrobe ESR by the Wintrobe anemia correction chart of the Hynes and Whitby method is presented. Although many significant correlations exist, only the Wintrobe and Westergren ESRs and plasma viscosity approached the same number of abnormal results. If the results of the Wintrobe and Westergren are combined 67 abnormal results are observed. The plasma viscosity exhibited a 10.4 percent false positive rate compared to the combined ESR's and a 6.0 percent false negative rate. The plasma viscosity was not only highly significantly correlated with the ESR's (P < < 0.001), but also with all acute phase reactants measured as well as total protein, albumin, and gamma-globulin. The plasma viscosity appears to give the best overall summation of the many non-specific changes observed in chronic disease.