Three human non-Hodgkin lymphomas of B-cell origin have been maintained as xenografts in artificially immunosuppressed mice. The long-term maintenance (3-5 years) resulted in no significant change in the morphology, DNA-index or cell surface markers of the tumors. Immunophenotyping revealed many similarities in the morphologically distinct lines. Light chain (lambda) restriction appeared in two lines (HT 58 and 130), but in the third line (HT 117) the co-expression of both light chains indicated the origin from light chain 'uncommitted' B cells. HT 117 was also different, expressing high transferrin-receptor activity, although it proliferates with practically the same rate as the other two lines. This study confirms the value of the xenograft system to approaching many tumor-specific problems.