The influence of glucose and substrates on sodium transport (TNa) and glucose transport (Tg) was studied in isolated rat kidneys perfused according to Bowman’s technique. Glucose (0–8 g/l) was added to the perfusion fluid in the presence or absence of substrates: i.e. 2·10-3M pyruvate, 2·10-3M lactate, 5.10-3M glutamic acid and 1·10-3M oxaloacetic acid. When glucose was used at different concentrations in the perfusate, a correlation was found between Tg and TNa (p < 0.001); when substrates were added, lactate was found to be the only substrate able to improve TNa significantly without affecting Tg. Fractional sodium reabsorption reached 98.54% when lactate and glucose (2 g/l) were present in the perfusion medium. The data suggest the existence of a link between TNa and Tg and the possibility of some dissociation betwee