Antigen presentation by macrophages is accompanied by the production of interleukin-1 (IL-1) for successful T cell triggering. We have described EBV infected B cell lines that served as antigen presenting cells (APC) and now report the ability of these cells and their supernates, as well as EBV negative B cell lines, to support IL-2 production by a T cell line JM in the presence of the monoclonal antibody that recognizes the CD3 complex. Both EBV-transformed B cell lines and EBV-negative lines, and their supernates, exhibited IL-1-like activity in two different IL-1 dependent assays. These IL-1-like molecules were released constitutively from five of six EBV positive lines and three of five non-infected B cell lines. The activity from both, one virally infected and one non-infected B cell line, eluted from Sephadex G-75 in two peaks at 15-18K and 30-35K and could not be neutralized by antibody specific for macrophage IL-1. Supernates having IL-1-like molecules also contained a higher molecular weight inhibitor of proliferation. These data indicate that: both EBV-positive and EBV-negative B cell lines are capable of elaborating the IL-1-like activity; and the IL-1-like activity from these cells can be serologically distinct from macrophage IL-1. This suggests the presence of a family of molecules with IL-1 activity that derive from different cell types.