In 31 patients with sudden isolated unilateral idiopathic lesion of the vestibular function the effect of therapeutic application of low molecular weight dextran and cortison was examined. 15 out of 31 patients received no drugs, 16 patients were treated with dextran-infusion and cortison for 10 days. Without drug application the vestibular function was restored in only 4 out of 15 patients after about 9 months, but after the therapeutic application of low molecular weight dextran and cortison a normal reaction of the vestibular system was seen in 11 out of 16 patients.