The effects of intraperitoneal administration of UDP-glucose were studied on male rat gastrocnemius muscle. Muscular glycolytic substrates and metabolites (glycogen, glucose, glucose-6-phosphate, pyruvate, lactate), Krebs' cycle intermediates (citrate, alpha-ketoglutarate, malate), related aminoacids (glutamate, alanine), ammonia, energy store and mediators (creatine phosphate, ATP, ADP, AMP) and the energy charge potential were evaluated. UDP-glucose was administered intraperitoneally at doses of 0.8, 2.0 and 5.0 mg/kg daily for 1, 2 and 4 weeks. The influence of the factors: "dose" of UDP-glucose and "time-course" of treatment was defined. After two weeks, the administration of the three doses tested of UDP-glucose changed the muscular concentration of few glycolytic metabolites, and of some Krebs' cycle intermediates, while after 1 or 4 weeks of treatment there was negligible response.