SJL/J lymphomas emerged as H-2Ds-negative variants upon transplantation of their respective H-2Ds-positive spontaneous tumors. Of nine spontaneous SJL/J lymphomas examined, only two contained detectable numbers of H-2Ds-negative tumor cells. Of seven successfully transplanted tumors, however, four emerged as predominantly H-2Ds-negative tumors by their second transplantation. Long term SJL/J lymphoma lines, RCS 5 and SJL/SJL, were also found to be H-2Ds-negative. The expression of H-2Ks and I-As were maintained on all tumor lines examined. H-2Ds-negative tumor cells were consistent stimulators of syngeneic lymphoproliferation, whereas tumors maintaining H-2Ds expression varied in their stimulatory capacity. Transplantation times required to achieve morbidity in syngeneic mice correlated with tumor cell expression of H-2Ds. Tumors maintaining H-2Ds expression were less aggressive and required 57 to 150 days to produce morbidity compared with highly aggressive H-2Ds-negative tumors that required only 7 to 10 days at one-quarter of the cell dose (10(7) cells). Growth curve analysis based on spleen weights (corrected for body weight) indicated that three types of SJL/J lymphomas could be identified based on their expression of H-2Ds and ability to stimulate syngeneic lymphoproliferation: 1) indolent, nonstimulatory H-2Ds-positive tumors; 2) indolent, stimulatory H-2Ds-positive tumors; and 3) highly aggressive, stimulatory H-2Ds-negative tumors.