Scatchard plot analysis of the binding of 125I-labeled C57A/N106S to freshly purified naive T cells, Ia+ cells, and NK1.1+ cells. Ninety percent of the total cells in the naive T cell fraction were CD4+ CD62Lhigh, 80% of the cells in Ia+ cell fraction were I-Ad+, and 92% of the cells in NK1.1+ fraction were NK1.1+, as determined by flow cytometry. Similar results were obtained in three experiments.