Adipogenesis plays a critical role in energy metabolism and is a contributing factor to the obesity epidemic. This study examined the proteome of primary cultures of human adipose-derived adult stem (ADAS) cells as an in vitro model of adipogenesis. Protein lysates obtained from four individual donors were compared before and after adipocyte differentiation by two-dimensional gel electrophoresis and tandem mass spectroscopy. Over 170 individual protein features in the undifferentiated adipose-derived adult stem cells were identified. Following adipogenesis, over 40 proteins were up-regulated by > or = 2-fold, whereas 13 showed a > or = 3-fold reduction. The majority of the modulated proteins belonged to the following functional categories: cytoskeleton, metabolic, redox, protein degradation, and heat shock protein/chaperones. Additional immunoblot analysis documented the induction of four individual heat shock proteins and confirmed the presence of the heat shock protein 27 phosphoserine 82 isoform, as predicted by the proteomic analysis, as well as the crystallin alpha phosphorylated isoforms. These findings suggest that the heat shock protein family proteome warrants further investigation with respect to the etiology of obesity and type 2 diabetes.