The Authors have analyzed the complex problems of the possible binding between uric acid and plasma proteins using two methods consisting of serum ultrafiltration at 22 degrees C or electrophoresis on different supports with successive specific coloration of the free and bound uric acid. The percentage of free and bound uric acid was established in serum from normal subjects, patients with primary gout, patients with renal insufficiency treated by dialysis and subjects with type IV dyslipidemia. The Authors discuss the results obtained as regards the possible role played by urate-plasma proteins binding in the interpretation of a genetic defect present in gouty patients involving a diminished uric acid binding capacity of plasma proteins.