The activity of rubber transferase (RuT) determined in washed rubber particle (WRP) and whole latex showed a marked increase in the advanced stages of tapping panel dryness (TPD) compared to healthy and early stages of TPD. Prenyl transferase activity measured in the C-serum of latex showed a slight decrease in the early stages of TPD, but was substantially large in the advanced stages of TPD. There was a positive correlation between RuT and prenyl transferase activities. The increased activities of RuT and prenyl transferase under in vitro conditions in presence of adequate conversion of their substrates suggest the presence of a large number of small rubber particles in a given unit weight of WRP. The mean rubber particle size slightly increased in the early stages of TPD, but was smaller in the advanced stages of TPD. The mean rubber particle size was negatively correlated with RuT activity. It is suspected that both RuT and prenyl transferase remained inactive under in vivo conditions possibly due to inadequate supply of their immediate substrates. These findings are discussed in the light of our earlier results that showed enhanced respiration in the TPD affected bark tissues.