To determine whether the characteristics of preadipocytes derived from human fat are uniform or variable, we developed methods for culturing and differentiating cloned human preadipocytes. Individual human omental preadipocytes were cultured for six weeks. The number of cells varied considerably among clones derived from the same subject, implying that human preadipocytes vary in replicative capacity. Indeed, two cell subtypes were found in human omental fat; one type replicated slowly and the other was capable of extensive replication. Cells of both subtypes were capable of differentiation into adipocytes, confirming that both subtypes were preadipocytes. When rat perirenal and epididymal preadipocytes were cloned, a slowly replicating and an extensively replicating preadipocyte subtype were also found. It is proposed that preadipocytes of the rapidly and the slowly replicating subtypes may be at different stages along the pathway between uncommitted precursor cells and differentiated adipocytes.