The authors analyse the case of a 58-year-old male suffering from substantially "atypical" multiple sclerosis (MS), both in terms of the late onset and because of some characteristics of the course of disease. The patient was treated with a subcutaneous immunomodulator (thymopentin) at a dose of 50 mg/day in 3-monthly cycles with intervals of 2 months between cycles, for a total of 3 cycles. Instrumental (CAT-NMR) and laboratory (immunological) tests were not significant, whereas others provided complex responses that allowed the presence of a demyelinating syndrome to be ascertained, above all due to the positivity of isoelectrofocusing. Treatment with thymopentin, commenced 12 years after the clinical onset of disease and after numerous cycles of cortisone and ACTH therapy, led to a major improvement in clinical conditions, especially of "sthenia" and movement, with consequent recovery of personal autonomy and working capacity which had previously been totally lost. Immunological tests performed at the end of each treatment cycle showed some slight but interesting modifications in parameters relating to DNA and the percentage of HLA antigens bound to lymphocytes. These findings suggest that the patient's immune system was sensitive to treatment with the thymic hormone responsible for the objective clinical improvement. These results appear to open the way to the possible treatment with immunomodulators.