In our previous study we found that the ARH 77 human B lymphoblastoid cell line, originating from a patient with multiple myeloma, produced both human interferon-alpha (HuIFN-alpha) and HuIFN-beta after induction with Sendai virus. In order to examine whether IFN-alpha-producing ARH 77 cell clones can be separated from IFN-beta-producing ones, the ARH 77 line was cloned by the soft agar method. Twelve clones chosen at random were examined for IFN production and the antigenic types of IFN produced were determined. All examined clones simultaneously produced both HuIFN-alpha and HuIFN-beta, although the ratio of HuIFN-alpha to HuIFN-beta production was variable among the clones. This result suggests that one lymphoblastoid cell can produce both HuIFN-alpha and HuIFN-beta.