Low molecular weight dextran (LMDx) was given by continuous intravenous infusion to cases of acute myocardial infarction in doses of about 2.0 g/kg/24 hours for 76 hours. In cases with good renal function and good renal perfusion, the 24 hour urine output was approximately 2 liters with a specific gravity around 1.040. In cases with chronic renal disease, the urine volume was often 2 liters or more but the urine specific gravity was consistently below 1.025. This was felt to be an indirect indication of inadequate renal excretion and justified a reduction in the input of LMDx. With reduced renal perfusion and normal kidneys, urine volume was reduced and specific gravity often greater than 1.065. This was associated in 6 cases with the appearance of spotty hydropic tubular changes in the kidneys and considered cause for reducing LMDx input.