Recent evidence has been presented that expression of lipogenic genes is down-regulated in adipose tissue of ob/ob mice as well as in human obesity, suggesting a functionally lipoatrophic state. Using ²H₂O labeling, we measured three adipose tissue biosynthetic processes concurrently: triglyceride (TG) synthesis, palmitate de novo lipogenesis (DNL) and cell proliferation (adipogenesis). To determine the effect of the ob/ob mutation (leptin deficiency), on these parameters, adipose dynamics were compared in ob/ob, leptin-treated ob/ob, food-restricted ob/ob, and lean control mice. Adipose tissue fluxes for TG synthesis, DNL and adipogenesis were dramatically increased in ob/ob mice compared to lean controls. Low-dose leptin treatment (2 µg/ day) via mini-osmotic pump suppressed all fluxes to control levels or below. Food restriction in ob/ob only modestly reduced DNL with no change in TG synthesis or adipogenesis. Measurement of mRNA levels in age-matched ob/ob mice showed generally normal expression levels for most of the selected lipid anabolic genes and leptin treatment had, with few exceptions, only modest effects on their expression. We conclude that leptin deficiency per se results in marked elevations in flux through diverse lipid anabolic pathways in adipose tissue (DNL, TG synthesis and cell proliferation), independent of food intake, but that gene expression fails to reflect these changes in flux.