This paper deals with the balancing problem of mixed-model flow lines for assembly. After formulating this problem under the constraint that the same work-element for different models must be allocated to the same station, a new heuristic procedure was presented. The procedure consists of three methods, weighing method, backtracking method and insertion-exchange method. A computer program was developed and applied to artificially made 72 problems. The quality of solutions and C. P. U. times were investigated. It revealed that the first two methods always succeeded in minimizing the numbers of stations for all of the problems, and that the 3rd showed significant improvement for the balance of each model. The C. P. U. time of the 1st method was considerably short, and that of the 2nd grew approximately in the order of K2 with the size (K) of work-elements, and in the order of W2 with the size (W) of the mean value of the numbers of work-elements allocated. to a station, while the time of the 3rd showed concave growth with the balance delay.