An analysis of the cell-surface expression of activation markers on B- and T-cells was done to compare patients with myasthenia gravis (MG) and healthy non-myasthenic controls. Marker expression was determined by immunostaining of peripheral blood mononuclear cells (PBMC) isolated from MG patients and from controls. The percentage of B-cells in PBMC that expressed CD71, a transferrin receptor, was significantly greater in patients compared to controls, particularly, in patients who were seropositive for acetylcholine receptor-specific antibodies. When subgroups of MG patients were studied, our data showed that within the first year after disease onset, patients had a significantly higher percentage of T-cells in PBMC that were CD25⁺ (interleukin-2 receptor α) and CD26⁺ (dipeptidyl peptidase IV ectoenzyme) in comparison to patients with disease symptoms for longer than one year and to healthy controls. Our data also showed that patients with generalized MG had significantly lower percentages of γ/δ T-cells in peripheral blood compared to healthy controls. The results of this study demonstrate important differences in the cell-surface expression of lymphocyte markers between MG patients and healthy non-myasthenic controls. In addition, differences between subgroups of patients demonstrate that patients with MG are heterogeneous in clinical presentation and in immunological parameters.