1. The structure of the products obtained from the reaction of NR latex with peracetic acid depends on the reaction conditions. 2. Under controlled conditions, specific levels of epoxidized NR (ENR) can be obtained. A random epoxide distribution has been observed. These materials undergo strain crystallization and hence exhibit good strength properties, although at high levels of epoxidation there is a decrease in the degree of crystal-unity. Other properties, e.g., hysteresis, air permeability, and oil resistance, change systematically with the level of epoxidation. These properties indicate that ENR has the potential to become an extremely useful commercial polymer. 3. At higher acid concentrations and/or temperatures, ring opening of the epoxide groups occurs, and even low levels of ring-opened structures have been found to adversely affect the properties of ENR. 4. The nature of the ring-opened structures depends on the degree of epoxidation. At low levels of epoxidation, where the majority of epoxide groups are isolated, simple diols and hydroxyacetates are formed. However, at higher epoxide levels, where blocks of epoxide predominate, the major product is a five-membered cyclic ether. At 100 mole% modification, a white amorphous thermoplastic product was obtained consisting almost entirely of furan structures.