Guillain-Barré syndrome offers the unusual opportunity of investigating the early stages of a monophasic autoimmune response. Créange et al (pp 162–5 of this volume) have shown that the concentration of the immunoregulatory cytokine transforming growth factor (TGF-β1) is decreased in Guillain-Barré syndrome at the time of presentation and increases after treatment with either plasma exchange or intravenous immunoglobulin. These results are in line with a previous report.1 They also confirm the previously reported increased concentrations of the inflammatory cytokine tumour necrosis factor α.2 Circulating …