A novel scan-line algorithm for displaying bicubic surfaces is presented. Patches are decomposed on regions of constant sign of the z component of the normal before the scan process. Most of the computations are done in parametric space. The algorithm computes the intersection of the surfaces with only a restricted subset of scan planes and obtains the intersection with other scan planes by linear interpolation between exact intersections. A bound of the algorithm's error is given. The method is compared with Whitted's algorithm.