The x-ray study of gutta-percha and balata has already been undertaken by G. L. Clark, E. A. Hauser, and his collaborators as well as by E. Ott. Their results are contradictory, however, in many respects. For example, Clark gives different values for the lattice of gutta-percha and for the lattice of balata, while Hauser has observed a difference for the angle of deviation only with stretched samples, and consequently proves that the position of the point interferences of the fiber diagrams is identical for both substances. Moreover Ott's values for gutta-percha vary greatly from those given by Clark. The roentgenographic observations referred to agree only in two respects: 1. Gutta-percha and balata are already crystalline in the unstretched state. 2. The lattice of gutta-percha and of balata is different from that of rubber. We have studied gutta-percha and balata by means of x-rays with the idea of clearing up the disagreements in previous publications and of determining whether or not there is any difference between gutta-percha and balata.