Following a transient rise at the early stage, the respiratory rate of tissues from young sugarcane leaf declined quickly during the enzymatic isolation of protoplasts. The respiration of freshly prepared protoplasts was inactivated by the cell wall degradation products (CWDP) which inactivated the activities of the key respiratory enzymes, suggesting that the decrease of respiratory activity might be caused mainly by the toxicity of CWDP during the enzymatic isolation of protoplasts. The activity of EMP in the freshly prepared protoplasts was similar to that in the intact tissue, but the TCAC activity was much weaker, whereas the pentose phosphate pathway activity was almost twice as strong as that in the intact tissues.