Two monoclonal antibodies (AD-1 and AD-2) were prepared by fusion of mouse myeloma cells and lymph node cells of mice immunized with porcine adipocyte plasma membranes. Immunoprecipitation of iodinated adipocyte plasma membrane proteins followed by SDS-PAGE and autoradiography yielded protein antigens for each antibody. The AD-1 and AD-2 antigens were detected on mature adipocytes and a proportion of non-lipid-containing cells in stromal-vascular cultures. Adipocytes and associated capillary networks in subcutaneous adipose tissues as well as capillaries between the underlying muscle fiber bundles bound each antibody, whereas the AD-2 monoclonal antibody also reacted with vessels but not capillaries in liver tissues. In stromal-vascular cell cultures prepared from newborn pig subcutaneous tissue, the AD-1 and AD-2 antibodies exhibited reactivity towards 45 percent and 10 percent respectively, of cells 24 hours after seeding. On the other hand, only 4 percent and 1 percent of the cells in cultures prepared from 60 day fetal subcutaneous tissues expressed detectable amounts of the AD-1 and AD-2 antigens, respectively. In conclusion, cells along the adipogenic lineage possess cell surface antigens which may not be unique to adipogenic cells, but do exhibit differential expression among cell populations within adipose tissues. A temporal relationship between adipogenesis and angiogenesis was also demonstrated.