Heat stress has a deleterious effect on the growth of broilers and early heat conditioning increases the ability of broilers to tolerate elevated temperatures in later life. One hypothesis is that embryonic heat conditioning alters gene expression patterns resulting in improved thermal resistance during subsequent growth. To test this hypothesis, we examined the transcriptome response of Ross 708 broilers to thermal conditioning and subsequent heat stress. Preliminary results characterizing the liver transcriptome of 42 day post-hatch birds suggest that embryonic heat conditioning elevates the level of hemoglobin mRNA during chronic heat stress. In addition, hierarchical clustering of the transcriptome data from right and left liver lobe samples indicates that the lobes from different individuals are more similar to one another than different lobes from the same individual. Inspection of the genes driving this clustering reveals that the left lobes express higher levels of mRNAs affecting oxidative phosphorylation. This difference was irrespective of heat conditioning or heat stress.