Peritoneal (PE) B cells, a large fraction of which belong to the B-1 subset (i.e., the CD5+ B cell lineage), exhibit unusual growth and/or survival characteristics. To evaluate if these characteristics reflect intrinsic properties of PE B cells or the support provided by a potentially unique peritoneal microenvironment, B cells from various organs were cultured on PE stromal cell monolayers. It was determined that sIgM+ PE B cell populations survive for notably long periods of time (at least 4 weeks) when cultured with PE stromal cells. Contact of PE B cells with stromal cell monolayers optimized B cell survival. Although expressing a similar spectrum of adhesion molecules as peritoneal stromal cells, splenic and bone marrow stromal cells were significantly inferior at supporting PE B cells. Increased survival of PE B cells was characterized by a significant but transient increase in proliferation and by an increase in the percentage of B220/CD45high/CD5+ PE B cells. PE stromal cell support of B cell populations did not extend to all B or even to all B-1 cell populations since survival of splenic B cells, only a minority of which belong to the B-1 lineage, or thymic B cells, a majority of which belong to the B-1 lineage, was not enhanced by culture on PE stromal cells. Results demonstrate: (a) a system for relatively long-term maintenance of mature B cells, (b) that the growth/survival of PE B cells is preferentially supported by PE stromal cells, and (c) that growth on PE stromal cells is a characteristic of peritoneal B cells but not necessarily of splenic B cells or B-1 cells from other organs. The suggestion that the local microenvironment contributes to unusual growth, survival, or anatomic distribution of B-1 cells is discussed.