Measurements of urinary lactate dehydrogenase (LDH) activity in 25 patients with clinically significant unilateral nephroptosis demonstrated a posture-dependent change. While these patients were supine – overnight – the urinary LDH activity was normal. On assuming an erect posture, the LDH activity rose to abnormal level. Such ‘swinging’ changes in urinary LDH activity could not be detected in normal people and in patients having undergone nephropexy one year following the intervention. The LDH activity obtained by unilateral catheterization was shown to be higher on the affected side than on the normal.