Endurance tests were carried out for rolling contacts of roller on roller, ball on saddle type specimen, and ball on ball, lubricating with machine oil. The limit values of their pitting strength indicated by Hertz's maximum pressure increased remarkably with the decrease of cling factors. In the case of rolling contact of ball on ball, the contact surface deformed plastically marking a flat band, and the logarithmic diagram of the width of this contact area versus repetition numbers was in linear relation. From this fact we can practically estimate the variation of maximum pressures acting on the curved surfaces. The fatigue diagram for the constant equivalent shear stresses calculated for these varying maximum pressures coincided with the fatigue diagram in the case of the constant shear stresses for the contact of rollers considered as a problem of plane strain. Applying these results, we have tried to explain the life of ball bearings.