Seven adult patients received human immune globulin intravenously as initial therapy for Guillain-Barré syndrome. Although all patients initially stabilized or improved, five patients deteriorated 1 to 16 days after completion of treatment. In all five patients, clinical worsening included loss of at least one functional grade together with a decreased forced vital capacity. We subsequently treated each patient with a course of plasma exchange, which led to varying degrees of clinical improvement in four. In contrast to previously reported relapse rates for Guillain-Barré syndrome, our experience suggests that clinically significant relapses may occur in patients more often following human immune globulin therapy than after either plasma exchange or no therapy.