Intrinsic viscosity and osmotic molecular weight data are presented for toluene solutions of several types of natural rubber after mastication in air. For [η] < ca. 4 all these data fit the relationship, [η] = 7.11 × 10−7 M̄n1.25. At higher molecular weights deviations from this relation are found, the extent of which depend on the type of natural rubber used. These deviations are attributed to differences in initial molecular weight distribution.