The presence of the oxidative reactions of the pentose phosphate pathway in hevea latex and their interaction with the biosynthesis of rubber are demonstrated using radioisotopes. During the second oxidation-reduction reaction of the pentose phosphate pathway the tritium in C-3 of glucose-6-phosphate is transported as tritiated nicotinamide adenine dinucleotide phosphate and serves to reduce [3-C-14] 3-hydroxy-3-methylglutaryl coenzyme A to mevalonate. Reduced nicotinamide adenine dinucleotide phosphate is the inter-connection between these two metabolic routes present in hevea latex, thus the hydrogens of glucose end up in rubber.