Abstract: The effects of respiratory inhibitors and various substrates on the biosynthesis of sucrose and the respiratory activity of Bai-Lan melon fruits were investigated. The content of organic phosphate and the rate of high-energy phosphate formation were also determined at different stages of fruit development. After infiltrating the fruit slices with inorganic phosphate and adenosine triphosphate, the rate of sucrose synthesis and the respiratory activity were increased to different extents, the effectiveness of ATP in increasing sucrose synthesis and respiration was higher than inorganic phosphate. Fruits at later stage of development showed a greater response to the above treatments than those at early stage. When KCN was added to the substrates, synthesis of sucrose and the intensity of respiration were reduced, but the fruits at early stage were more susceptible to it than those at later stage. The content of organic phosphates and the rate of high-energy phosphate formation were higher in fruits at later stage than those at early stage. The above results show that phosphorylation is closely connected with .the synthesis of sucrose in fruits at both stages of development. The low rate of phosphorylation is, however, not the principal factor responsible for the lower capacity of sucrose synthesis in fruits at early stage. It is very possible that the metabolic mechanism is different at different stages of development and it is this mechanism which allows the energy and metabolites to be flowed into canals of growth and associated processes in fruits at early stage, and to be switched to canals of sucrose synthesis and related processes at later stage of fruit development. The implications of this suggestion is briefly discussed.