The influence of long-term corticosteroid and ACTH therapy in two sisters was followed up. The periods of observation were 4 and 2 years. The high levels of corticosteroids obviously reversed the fatal progress of the disease. The relapses in the elder sister occurred during longer periods of discontinued corticosteroid therapy. In the younger the therapy was continuous. There was no relapse except for a short one appearing after the tooth extraction and discontinuation of the therapy for 10 days. Some correlation between neurological signs and symptoms and porphobilinogen and uroporphyrin levels were found. The question arises how it is possible to influence the genetically determined disease by corticosteroids or ACTH.