IL-3-dependent cell line (designated as A-3) from adherent spleen cells was developed. The surface phenotype of A-3 cells was analysed by flow cytometry and determined as ASGM1+, FcR+, Ia+. There was no expression of T cell markers (Th1-CD3-CD4-CD8-), B cell marker (surface Ig) as well as macrophage marker Mac-1 antigen. Although A-3 cells expressed ASGM1, they are lacking NK cytotoxic activity in 4 h Cr release assay with YAC-1 targets. In contrast, A-3 cells are endowed with NC cytotoxic activity as shown in 18 h Cr release assay with WEHI-164 target cells.