This is a multinational, multicenter, randomized, double-blind, parallel-group, placebo-controlled study followed by active treatment, to evaluate the efficacy, safety and tolerability of two doses of oral administration of laquinimod in subjects with RRMS. . The study has periods: Period 1, the double-blind, placebo-controlled period (up to 24 months) and Period 2, the active treatment period (24 months).