Multiple sclerosis is probably mainly mediated by T-helper 1 (T(H)l)-lymphocytes. T(H)1-function can be down-regulated in vitro and in animal experiments by pentoxifylline. Therefore, we included 20 multiple sclerosis patients in an open label pilot trial of pentoxifylline. Ontcome parameter was the effect of treatment on levels of various cytokines and adhesion molecules in cerebrospinal fluid and serum, on production of T(H)1- and T(H)2-cytokines using cell stimulation assays, as well as on measures of T-cell activation and proliferation. Kurtzke's EDSS was a secondary efficacy parameter. A convincing and consistent effect of pentoxifylline could not be demonstrated.