Catecholamine content and in vitro activities of tyrosine hydroxylase (TH) and noradrenaline N-methyltransferase (NMT) were measured in cultures of isolated adrenal medullary cells from newborn and young postnatal rats to study the effects of the differentiation factors glucocorticoids and nerve growth factor (NGF). During the 4-day culture period the cellular catecholamine (CA) content and TH activity remained stable, whereas NMT activity dropped to about half of the initial level. In cells from 2- and 10-day-old rats 10 microM dexamethasone specifically prevented this loss in NMT activity. Furthermore, this glucocorticoid treatment increased, in a dose-dependent manner, the total CA content by 50-100% over control levels without changes in the adrenaline (A) proportion or TH activity. In contrast, NGF did not affect NMT activities at all. In cells from 10-day-old rats 100 ng/ml NFG elevated TH activity and total CA content to about 160% of controls and did not change the proportion of A. This increase in total CA content was linear with the NGF dose and required greater than 5 ng/ml NGF. In chromaffin cells from 2-day-old rats 100 ng/ml NGF affected neither TH activity nor the total content, whereas it significantly reduced the proportion of A by about 25%.