Humoral and cellular immune factors were studied in 33 newly diagnosed Graves' patients at diagnosis and in 12 of these patients at regular intervals thereafter. All the patients were treated with carbimazole for 15 months (initially 60 mg and then 20 mg supplemented with L-Thyroxine). The incidence of relapse after treatment was 42%. Thyrotropin receptor antibodies (TRAb), T-cell subsets, K and NK cells and mononuclear cells expressing surface antigen markers of different activation were evaluated respectively by the use of a radioimmunoassay and a panel of monoclonal antibodies. Patients in the follow-up study were HLA-A, B, C and D typed. TRAb levels (91%) and levels of 4F2-positive cells (73%) and class II-positive lymphocytes (69.6%) were significantly increased in newly diagnosed Graves' patients in comparison with normal controls, whereas CD8 cells were significantly decreased. There was a significant inverse correlation between the increase in 4F2-positive cells and TRAb values. In the follow-up study both humoral and cellular immunological parameters showed a wide variation in levels, but TRAb, 4F2 and L243 values declined on average with respect to diagnosis. After 15 months some patients still showed abnormal values of activated T cells and TRAb values. All patients who relapsed (42%) after medical treatment showed a significant increase of 4F2-positive cells, and some of TRAb, some time before the appearance of clinical symptoms. Finally, no correlation was found between HLA type and relapse of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)