A patient with Guillain-Barré syndrome is reported on who responded favourably to a short course treatment with the novel immunosuppressant sodium fusidate (Fucidin), given at a daily dose of 1.5 g for one week. Along with prompt and clear cut clinical improvement, treatment with Fucidin was associated with a rapid decline in the blood concentrations of inflammatory cytokines presumably implicated in the pathogenesis of Guillain-Barré syndrome such as interleukin-2, interferon-gamma, and tumor necrosis factor-alpha. The ex vivo production of these cytokines was also markedly diminished compared with pretreatment values. Fucidin was well tolerated and no clinical or biochemical side effects were seen.