Rapid growth is of crucial importance for Adelie penguin chicks reared during the short antarctic summer. It partly depends on the rapid ontogenesis of fat stores that are virtually null at hatching but then develop considerably (x 40) within a month to constitute both an isolative layer against cold and an energy store to fuel thermogenic and growth processes. The present study aimed at identifying by RT-PCR the major transcriptional events that may chronologically underlie the morphological transformation of adipocyte precursors into mature adipocytes from hatching to 30 days of age. The peak expression of GATA3, a preadipocytes marker, at day 7 indicates a key proliferation step possibly in relation with the expression of C/EBP. High plasma total T₃ levels and high levels of GH receptor transcripts at hatching suggested that GH and T₃ may play early activating roles to favour proliferation of preadipocyte precursors. Differentiation and growth of preadipocytes may occur around day 15 in connection with increased abundance of transcripts encoding IGFI, PPAR and C/EBP gradually leading to functional maturation of metabolic features of adipocytes including lipid uptake and storage (lipoprotein lipase, fatty-acid synthase) and late endocrine functions (adiponectin) by day 30. Present results show a close correlation between adipose tissue development and chick biology and a difference in the scheduled expression of regulatory factors controlling adipogenesis as compared with in vitro studies using cell lines emphasizing the importance of in vivo approaches.