CD4⁺CD25^highCD127^low/– forkhead box p3 (Foxp3)⁺ regulatory T cells (T_reg cells) possess functional plasticity. Here we describe a higher frequency of T helper type 1 (T_H1)-like, interferon-γ (IFN-γ)-secreting Foxp3⁺ T cells in untreated subjects with relapsing remitting multiple sclerosis (RRMS) as compared to healthy control individuals. In subjects treated with IFN-β, the frequency of IFN-γ⁺Foxp3⁺ T cells is similar to that in healthy control subjects. In vitro, human T_reg cells from healthy subjects acquire a T_H1-like phenotype when cultured in the presence of interleukin-12 (IL-12). T_H1-like T_reg cells show reduced suppressive activity in vitro, which can partially be reversed by IFN-γ–specific antibodies or by removal of IL-12.