The articles in Issue 4 of JOURNAL OF INHERITED METABOLIC DISEASE, Volume 16 (1993) contain the main lectures presented at the 30th Annual Symposium of the Society for the Study of Inborn Errors of Metabolism (SSIEM), Leuven, Belgium, 1992, which was dedicated to `Inherited Metabolic Diseases and the Brain'. Topics discussed included: Inborn errors and brain fluids, neurotransmitter disorders, inborn errors and demyelination, and recent developments. Participants from many countries provided a state-of-the-art review which will be of interest to clinicians and research workers alike in many different disciplines.