Ethephon, an ethylene generator, is applied to the bark of rubber trees to increase natural rubber production by stimulating both latex flow and regeneration. A good command of both ethephon concentration and its frequency of application is required to avoid an oxidative burst into latex cells resulting in tapping panel dryness (TPD) and a loss of production. Although a little is known about the molecular response to ethylene stimulation further studies on ethylene biosynthesis and its regulation were needed to gain a better understanding of the mechanisms involved in latex production. The ethylene biosynthesis pathway is well characterised in many plant species. Sadenosyl- methionin (SAM) is produced from the methionin (Met) by the enzyme SAM synthase. Then, SAM is converted in 1-aminocyclopropane-1-carboxylic acid (ACC) by the ACC synthase (ACS) (Kende, 1993; Yang & Hoffman, 1984). ACC is converted to ethylene by the enzyme ACC oxidase, the production of which is also highly regulated. These three enzymes are encoded by a multigene family and their expression regulated differentially by various developmental, environmental and hormonal signals (Barry et al., 2000; Ge et al., 2000; Hacham et al., 2007; Llop-Tous et al., 2000) Several genes involved in the ethylene biosynthesis were previously isolated in rubber tree from cDNA library screening or PCR amplification of conserved regions using degenerated primers then RACE extension technology (Kuswanhadi, 2006). A differential gene expression was observed during plant development (Kuswanhadi et al., 2005) and a kinetic in response to ethephon, ethylene and wounding in 3-month-old budded plants (Kuswanhadi et al., 2006). In this study, we have monitored the expression of eight genes encoding four enzymes (SAMS, ACS, ACO and ßCAS) by real-time RTPCR. These expression levels in bark tissues of budded plant 3-month-old flushes were compared from three Hevea clones with contrasting metabolism. The variation in gene expres