The gravitational distortion effect of a nearby quasar on the image of a distant quasar in nearly the same direction is discussed as a method for estimating the mass of the nearer quasar. Account is taken of the effect of a cluster of galaxies in which the nearer quasar may be situated. Such ''optically double'' quasars yield upper mass limits when the image of the distant quasar is not completely resolved. The pair 1038+528 is considered as an example of the method and yields a limiting mass of 7 x 10/sup 13/ M/sub sun/ for simple assumptions, consistent with the estimate of Bahcall and Tremaine.