In 28 patients predialysis plasma myoinositol was significantly elevated to 10.8 ± 2.: versus 0.75 ± 0.15 mg/100 ml in normals (mean ± 1 SD), and was weakly correlated with plasm; creatinine concentrations (r = 0.42, p < 0.05). Dialysis decreased plasma myoinositol con centrations to 3.5 ± 1.1 mg/100 ml. In 16 patients studied more extensively plasma myoinosito was similarly elevated to 10.6 ± 3.4 mg/100 ml, and spinal fluid myoinositol was increased t < 9.4 ± 2.3 mg/100 ml (versus 2.7 ± 0.7 in normals, p < 0.001). Nerve conduction velocities wer reduced in 15 and EEG tracings were abnormal in 12 of the 16 patients. However, neither spins fluid nor plasma myoinositol showed any correlation with nerve conduction velocities or EEG changes (r = 0.05–0.20, NS) Myoinositol is one of the substances retained in renal insufficiency but no indication was found that it is a toxin causing uremic neurological disturbances.