We present two cases of Guillain-Barré syndrome (acute idiopathic neuritis) that developed after heart transplantation involving immunosuppression with cyclosporine, azathioprine, and steroids. The literature contains only two previous reports of posttransplant Guillain-Barré syndrome, both involving patients maintained with azathioprine and steroid immunosuppression after kidney transplantation. In our two cases (and in one of the previous cases), the syndrome was preceded by a sudden increase in the amount of serum immunoglobulin M antibody to cytomegalovirus. One of our patients improved neurologically after plasmapheresis, but neither patient appeared to benefit from the administration of gamma globulin. Because further immunosuppression would predispose the transplant patient to other opportunistic infections, we advocate a trial of plasmapheresis in the treatment of Guillain-Barré syndrome in this population.