AbstractWe examined alkaline phosphatase (ALPase)‐positive reticular cells from chicken bone marrow in vitro in relation to other varieties of adherent cells.ALPase activity was found in both reticular and adipose cells which formed epithelioid cell colonies and were negative for fibronectin. We observed transition between two cell types. ALPase‐negative macrophages as small round cells in culture revealed positive fibronectin and transformed into ALPase‐negative spindle cells in long‐term culture. Thus, we suggest two cell lineages, each with distinct cell characte