Sequential extraction of rubber particle proteins resulted in enrichment of 23.6 and 27.3 kDa rubber elongation factors. The 23.6 and the 27.3 kDa rubber elongation factors are highly similar in amino acid sequences. Subcellular localization results may be helpful to elucidate the function of rubber elongation factors. We suggested that REF/SRPP isoforms are structural proteins in rubber particles of H. brasiliensis.