In three-dimensional surface display, the grey-level values of the voxels on the surface of an object are not always constant . This fact means that the traditional grey-level gradients are not the exact representation of the surface normals. In this note we present an improved method of estimation of surface normal for 3D surface display. The new method calculates gradient at the location where the grey-level is equal to threshold value. Using this scheme, the gradients are estimated on an isogrey-level curve and are the exact surface normals. The images generated using this method show very fine details. The validity of the proposed scheme b illustrated with a number of examples * from medical imaging. The results are compared to images rendered by the traditional grey-level gradient method. ?he proposed algorithm has advantages over the traditional method in improved estimation of surface normal and rendering of finer details.