Peripheral blood cells of a patient with diffuse large cell non-Hodgkin's lymphoma presenting with hypereosinophilia were used to establish an EBV negative lymphoma cell line termed OCI-Ly17. Cells of the line stained positive for CD2 and CD5 determinants and demonstrated rearrangement of the T-cell receptor beta chain. The immunoglobulin heavy chain gene was found to be in germ line configuration. Northern blot studies using probes for IL-1 alpha, IL-3, IL-4, IL-5, IL-6, and GM-CSF showed message for IL-5 and IL-6. Supernatants of the cell line were evaluated on normal non-adherent, E-rosette depleted bone marrow cells to determine the presence of growth promoting activities for clonogenic eosinophilic progenitors. Eosinophilic colonies were observed. Their frequency depended upon the amount of supernatant added to the cultures. The growth promoting activity in the supernatant was reduced in a dose dependent manner by preincubation with increasing concentrations of anti-IL-5 antibodies. The supernatants of the cell line were also tested on the IL-6 sensitive human myeloma line OCI-My4 and myeloma colonies grew in response. This stimulatory activity within the supernatant was neutralized by addition of increasing concentrations of anti-IL-6 antibodies. Although producing IL-5 and IL-6 constitutively, the lymphoma line did not increase proliferation in response to either interleukin, nor did it show a reduced proliferative rate when antibodies to IL-5 or IL-6 were added to the cultures.