Binding of mebeverine-HCl and drotaverine-HCI to plasma proteins taken from healthy volunteers and from patients with renal failure was investigated using equilibrium dialysis technique. The concentration of total protein and albumin were determined. The study showed that the mean plasma albumin concentration was 4.3 gm% in the case of normal volunteers, and was 2.8 % in the case of patients with renal failure. On the other hand, the mean total protein concentration in plasma of normal volunteers was 6.5 %, and was 5.6 % in the case of plasma proteins of patients with renal failure. Binding study showed that the percentage bound of mebeverine-HCl was 83.51 in normal volunteers and 74.32 in patients with renal failure. The percentage bound of drotaverine-HCI was 72.45 in normal volunteers and 63.21% in patients with renal failure. This must be taken into consideration during the adjustment of the dose of both drugs.