Young postweaning pigs were fed a high fat diet containing beef tallow (saturated fat) or corn oil (unsaturated fat). Adipose tissue was used to measure adipocyte size and number of cells per gram of tissue, ligand binding by beta-adrenergic receptors and lipolytic and palmitate esterification rates. Pigs fed the saturated fat diet had more saturated and monounsaturated fatty acids and less polyunsaturated fatty acid in the crude membrane fraction. Adipocytes were larger in pigs fed the saturated fat diet. There was no difference in the binding affinities of the receptors; more binding sites were expressed on a protein or cell basis and fewer sites were expressed per unit surface area in adipocyte ghosts isolated from pigs fed the saturated fat diet. Fatty acid esterification was greater in pigs fed saturated fat diets. Isoproterenol inhibition was marginal in both groups but tended to be greater in pigs fed saturated fat diets. The beta-adrenergic receptor-mediated lipolytic rates were not different; only the theophylline-stimulated rates tended to be greater in the saturated fat-fed group. Thus, a large increase in saturated fatty acid concentration of porcine adipose tissue membranes caused an increase in beta-adrenergic receptor number without any change in receptor affinity. These receptor changes were at best only marginally reflected in beta-adrenergic agonist-mediated functions.