The case of a 6 1/2 year old boy with a severe nephrotic syndrome unresponsive to corticotherapy is described; hemodialysis was necessary one year after detection of the nephrosis. Because of clinical symptoms of hypothyroidism, thyroid function was evaluated during the different steps of nephrosis and hemodialysis. Total protein and iodine, albumin, thyroxine binding protein, free and total thyroxine, triiodothyronine and thyreostimuline determinations were performed in serum and/or urine. Thyroid hormone concentrations were very low during the nephrotic syndrome: they increased slightly when hemodialysis was started. Thyreostimuline values did not seem dependent on hormone concentrations. Thyroxine excretion was very much increased when compared to that of normal children, a finding present at all times.