Split Products of Fibrin (SPF) were determined by the tanned red-cell hemagglutination inhibition assay in 331 patients with various types of renal disease. The study included 77 sex-age matched controls. The mean value for SPF in the control group was 4.55 ± 2.46 S. D.SPF were elevated in the Hemolytic-Uremic Syndrome (1/1), Lupus Erythematosis (SLE) (8/10), Steroid Resistant Nephrosis (SRN) (7/13), Acute Glomerulonephritis (AGN) (13/26), Steroid Dependent Nephrosis (SDN) (8/32), Renal Vein Thrombosis (3/3), Hereditary Nephritis (4/15), Active Anaphylactoid Purpura (2/3), and Hypocomplementaremic Nephritis (1/3).To a lesser degree, the SPF were elevated in Steroid Sensitive Nephrosis (1/14), Idiopathic Hematuria (3/23), Post Acute Anaphylactoid Purpura (1/14), Post Acute Glomerulonephritis (2/20), Acute Urinary Tract Infection (2/18), and Post Urinary Tract Infection (2/81).No elevation in the SPF was noted in Orthostatic Proteinuria (16), Idiopathic-Hypertension (15), Single Kidney (15), Hydrone-phrosis (9), and Chronic Glomerulonephritis without Azotemia (14).A depressed Beta 1 C/Beta 1 A was closely correlated with the SPF in SLE (9/10) and AGN (24/26). Positive immunofiuorescent staining of renal biopsy tissue for at least one immunoglobin was correlated with an elevated SPF in SRN (6), SLE (5), AGN (5), and SDN (3). Immunoflourescent stains for fibrinogen were seldom positive. These data indicate that SPF are not diagnostic, and may be elevated in several types of renal disease.