Starch concentration, sequence of appearance of sucrose, glucose and fructose and activity of some enzymes of sucrose synthesis were followed during ripening of preclimacteric bananas (Musa acuminatd). As starch was degraded sucrose content increased and preceded formation of glucose and fructose. At the same time, while UDP-glucose pyrophosphorylase activity remained constant, activity of sucrose synthetase and invertase increased. The observed sugar and enzyme changes indicated that starch to sucrose transformation via glucose-1-phosphate-UDP-glucose may be an important mechanism for starch disappearance during ripening. The hypothesis was confirmed with thin banana slices infiltrated with [14C(U)]glucose-1-phosphate: the label was incorporated into sucrose three times faster for climacteric than for preclimacteric fruits. Pyrophosphorylase activity and climacteric induced activation of sucrose synthetase could be inhibited by protein and nucleic acids synthesis inhibitors.