Stearoyl-CoA desaturase (SCD) is a microsomal enzyme involved in the biosynthesis of oleate and palmitoleate. Mice with a targeted disruption of the SCD1 isoform (SCD1-/-) exhibit reduced adiposity and increased energy expenditure. To address whether the energy expenditure is attributable to increased thermogenesis, we investigated the effect of SCD1 deficiency on basal and cold-induced thermogenesis. SCD1-/- mice have increased expression of uncoupling proteins in brown adipose tissue (BAT) relative to controls. The beta3-adrenergic receptor (beta3-AR) expression was increased and the phosphorylation of cAMP response element binding protein and the protein level of peroxisome proliferator-activated receptor-gamma coactivator-1alpha were increased in the SCD1-/- mice. Both lipolysis and fatty acid oxidation were increased in the SCD1-/- mice. When exposed to 4 degrees C, SCD1-/- mice showed hypothermia, hypoglycemia, and depleted liver glycogen. High levels of dietary oleate partially compensated for the hypothermia and rescued plasma glucose and liver glycogen. These results suggest that SCD1 deficiency stimulates basal thermogenesis through the upregulation of the beta3-AR-mediated pathway and a subsequent increase in lipolysis and fatty acid oxidation in BAT. The hypothermia and hypoglycemia in cold-exposed SCD1-/- mice and the compensatory recovery by oleate indicate an important role of SCD1 gene expression in thermoregulation.