A perfused preparation of the hind limb of normal and diabetic rats was used to study the effects of lactic acidosis, alone or associated with hypoinsulinemic diabetes, on the incorporation of glucose and inorganic orthophosphate (Pi) into the skeletal muscle. A well oxygenated perfusate was recirculated for ninety minutes during which the lactic acid accumulated into the medium with the ensuing pH drop. The perfusions were practiced in the hind limb of alloxanized diabetic rats, in the hind limb of diabetic rats with perfusate containing 200 microU of insulin/ml, in the hind limb of 24 hour fasted rats, and on the hind limb of fed rats, and they were compared to similar groups with normalized pH perfusate with a sodium bicarbonate infusion. In the diabetic perfusions with lactic acidemia, it was observed that the addition of insulin increased the uptake of Pi and of glucose, and reduced the release of Pi by the muscular tissues. A smaller release of Pi by the preparations obtained from fed rats was observed when compared to the hind limb preparations of fasted rats. The diabetic preparations showed an increased glucose uptake when the pH was normalized, and a decrease of Pi released by the muscles, even in the absence of insulin, and at the same time, the administration of insulin associated with the normalization of pH increased the uptake of Pi and of glucose, and decreased the Pi released by the muscles. In all the groups, the administration of sodium bicarbonate significantly increased the lactate release into the medium. It was also found that the lactic acidosis reduced the uptake of Pi by the preparations inducing hyperphosphatemia. According to these results, muscular tissue plays a role in the hypophosphatemia that has been reported in the insulin treated diabetic ketoacidosis by increasing the incorporation of Pi and reducing its release by the same tissue.