Natural rubber (NR) from Hevea brasiliensis was found to be a polyisoprene comprising two trans-isoprene units and a long sequence of cis-isoprene units, The structural evidence showed that the rubber formation starts from C-15-trans-trans-farnesyl diphosphate (FDP) followed by biochemical modification at the dimethylallyl group or starts from a derivative of FDP, The bimodal molecular weight distribution of NR was presumed to be due to biodynamic origin and not to branching only, A deproteinization process of NR reduced the gel content to 1 to 2%, but did not affect the green strength nor other vulcanizate properties.