The physiological changes in the onset and development process of whole-cut dryness were investigated on Hevea trees of clones RRIM 600 and PR 107 under conventional tapping system. The dryness incidence and expansion rate of clone RRIM 600 are more than double when compared with clone PR 107. Some affected trees displayed a short time increase in initial flow rate and latex yield prior to dryness. The latex inorganic phosphorus (Pi) content increased considerably in the course of the onset and development of dryness. All the affected trees had a low latex sucrose content before the occurrence of drryness. Some affected trees had an elevated content of thiols (R-SH) before dryness occured but no abnormal regeneration of latex was observed. This paper also discuss the possible causes of rapid whole-cut dryness on rubber trees.