Infection elicits CD4(+) memory T lymphocytes that participate in protective immunity. Although memory cells are the progeny of naive T cells, it is unclear that all naive cells from a polyclonal repertoire have memory cell potential. Using a single-cell adoptive transfer and spleen biopsy method, we found that in mice, essentially all microbe-specific naive cells produced memory cells during infection. Different clonal memory cell populations had different B cell or macrophage helper compositions that matched effector cell populations generated much earlier in the response. Thus, each microbe-specific naive CD4(+) T cell produces a distinctive ratio of effector cell types early in the immune response that is maintained as some cells in the clonal population become memory cells.