Guinea pig IgG2 anti-idiotypic antibody (aId2) against the strain A/J antibody A5A has a suppressive effect on the expression of the A5A idiotype in adult A/J mice immunized with Group A streptococci. High doses of aId2 cause an immediate but transient suppression, whereas low doses of aId2 result in a delayed but chronic suppression which lasted for more than 1 year without any indication of recovery. Chronic suppression is transferred by as few as 10(5) spleen cells, but an interval of 6 weeks after transfer is required for completion of suppression. The suppressive capacity of aId2-induced suppressor cells was virtually inexhaustable in 4 consecutive transfers spaced at 3 month intervals. The suppressor cell is a T cell which adheres to histamine-rabbit serum albumin-Sepharose 2B columns.