Rate of dark respiration was measured in the soft bark tissue of ten clones of Hevea and related to the biochemical composition of the tissue and the dry rubber yield and biomass of the trees. The rate of respiration showed a positive correlation with total proteins, soluble sugars and starch contents in the laticiferous tissue. Tapping increased the rate of respiration in the bark. There was a positive correlation between the rate of respiration and the latex yield on a given day, indicating that a high respiratory activity was required to sustain high yield. Tapping led to substantial loss of biomass in all the clones and this was positively associated with dry rubber yield. There was more than proportionate loss of biomass as the annual mean dry rubber yield increased among the clones. This unaccountable loss of biomass could possibly be due to an increase in the maintenance respiration in the bark tissue of the high yielding clones which may be metabolically more active to sustain a high yield. Thus, it appears that the high yielding clones in general have poor efficiency in covering biomass into rubber.