White adipose tissue is a rich source of angiotensinogen protein and mRNA. Studies in clonal cells suggest that angiotensinogen, and its cleavage product, angiotensin II, are involved in preadipocyte differentiation into mature fat cells. No studies have determined whether angiotensinogen is also involved in adipose tissue development in vivo. In this report, we studied male Wistar rats at two stages of development to determine if angiotensinogen protein and mRNA are increased in retroperitoneal fat depots of rapidly growing young, lean, 8-week-old rats compared to 26-week-old rats that are fatter, but are undergoing less rapid adipose tissue growth. We also assessed renin mRNA and angiotensin I-generating activity, since it is less clear whether renin is locally produced in adipose tissue. We found that angiotensin I-generating activity was measurable in adipose tissue and adipocytes, but renin mRNA was undetectable by northern blot analysis. Angiotensinogen mRNA was abundant in adipocytes, but was absent in stromal-vascular cells of adipose tissue. Angiotensinogen content per 10 million fat cells was approximately threefold higher in 8-week-old rats compared to 26-week-old rats (p < .0002). Angiotensinogen mRNA was approximately twofold higher in adipocytes of 8-week-old rats compared to 26-week-old rats. The age-related decline in angiotensinogen protein and mRNA indicates that the local renin-angiotensin system may play an important role in adipose tissue growth, and possibly contribute to the changes in adipose mass and cellularity seen in old senescent rats.