We report on 7 patients suffering from chronic renal failure (2 females, 5 males; aged 35-75 (phi 53.5) years) who showed severe neuromyeloencephalopathy (NME) after high doses of a new Henle's loop diuretic, Muzolimine. The temporal and phenomenological development of these systems was strikingly parallel. The neurological deficit was revealed on neurophysiological, neuroradiological and in 2 cases on neuropathological tests (gross demyelinisation of the posterior column, mainly of the fasciculus gracilis, less in the lateral corticospinal tract and in some spinal roots). The critical drug dose for first neurological impairment was 52 g on average; at this point the patients had been treated for 78 days. The maximal daily dose was 1.440 mg. Dominant clinical features were pallhypaesthesia, ataxia, signs of peripheral neuropathy in combination with hyperreflexia and progressive para- to tetraspastic paresis. Constellation of symptoms, course of disease and findings of additional investigations, especially those of neuropathology, very much resemble Vitamin B12 deficiency and SMON-(Subacute Myelo Optic Neuropathy) syndrome. The rare entity of Muzolimine-NME is discussed in respect to other endogenous and exotoxic neuromyelopathies. We present the hypothesis of a toxic, partially dialysable metabolite of Muzolimine.