Abstract: A screening method for detecting renal lesions in diabetic patients not yet exhibiting symptoms of nephropathy, comprising administering a predetermined dose of parathyroid hormone, analogue thereof or derivative thereof to the patients with an albumin excretion rate (AER) of microalbumin being below 15 .mu.g/min., measuring urinary excreted N-acetyl-.beta.-D-glucosaminidase (NAG) and urinary creatinine in urinary samples taken 60.+-.10 minutes before and after administration of PTH, and monitoring the increased ratio of urinary excreted NAG (U/g Cr) in post-administration of PTH to the urinary excreted NAG (U/g Cr) in pre-administration of PTH for a value less than 2.3. The screening method provides the possibility of detecting renal lesions without clinical signs of diabetic nephropathy, using a preparation essentially consisting of active ingredient of PTH.