Inositol seems to play a role in the development of the central nervous system. In this study, the brain tissue level of inositol in fetal hydrocephalus was compared with that of healthy control subjects.Proton magnetic resonance spectroscopy was used to examine the inositol over creatine ratio in the brain of 10 hydrocephalic human fetuses and 36 normal control subjects.Resolved signals for inositol and creatine were detected successfully in six hydrocephalic fetuses and in all control subjects. The inositol over creatine ratio was significantly lower in fetuses with hydrocephalus (P <.01).This result supports speculations concerning the role of inositol in central nervous system development.