Lymphocyte migration into the central nervous system is a central event in lesion formation in multiple sclerosis. By using a fibronectin-coated membrane Boyden chamber assay, we observed that migration rates of immediately ex vivo lymphocytes from patients with relapsing-remitting, with or without concurrent clinical relapse, or with secondary progressive disease, were increased compared with healthy donors. Migration rates of lymphocytes from relapsing-remitting multiple sclerosis patients receiving either glatiramer acetate (Copaxone 20 mg daily) or interferon-beta1b (Betaseron 8 MIU, three times per week) were significantly reduced compared with untreated relapsing-remitting patients. In vitro treatment with interferon-beta1b (1,000 U/ml), but not glatiramer acetate (20 microg/ml), significantly reduced lymphocyte-migration rates, suggesting that the effects of these two therapeutic agents on migration result from different mechanisms of actions. Interferon-beta1b acts, at least in part, by a direct effect on this cell property, whereas glatiramer acetate effects are indirect.