The consequences of hyperlipidic feeding on interscapular brown adipose tissue (IBAT) activity were examined in the cold-acclimated rat. Male Osborne-Mendel rats (7 weeks old) were exposed for 10 weeks at either 28 or 5 °C. The rats were fed a semipurified diet (normal fat (NL): 5 % lard; high fat (HL): 54% lard) for the last 9 weeks. IBAT weight was greater in HL than in NL rats. This increase was entirely due to accumulation of neutral lipids. Among different IBAT components (proteins, DNA, phospholipids) no variations were observed in HL 28 °C rats. HL diet did not modify lipoprotein lipase and cytochrome oxidase activities, but an increase in purine nucleotide binding (taken as an index of thermogenic activity) was observed in HL 28 °C rats. Cold acclimation led to comparable stimulation in NL and HL rats. The calorigenic effect of norepinephrine in vivo was not modified by HL diet. Study of arteriovenous differences showed that IBAT fatty acid and glycerol release by norepinephrine was slightly increased in HL 28 °C rats. No effect of HL diet was observed at 5 ° C. These results indicate that HL feeding leads to a moderate increase in the IBAT thermogenic capacity of Osborne-Mendel rats. HL diet does not modify the normal development of nonshivering thermogenesis when rats are kept in a cold environ