The study of the control of aldosterone synthesis and secretion by the rat adrenal gland has over the past thirty years involved the application of many different in vivo and in vitro techniques. In this review the relationship between the data that each of these methods has produced is compared. There are striking differences in overall steroid production rates, and in the qualitative nature of the steroid profile which the various methods produce. In particular, aldosterone is secreted at higher rates in vivo, and when whole tissue preparations are used in vitro, than in incubations of isolated glomerulosa cells. In addition, while corticosterone is a major product of glomerulosa tissue in vitro, the available evidence suggests that it is not a major glomerulosa product in vivo.