The effect that several substances may have on ANF release by atrial slices and on its tissular content was investigated. alpha- and beta-adrenergic and cholinergic agonists, vasopressin, met-enkephaline, dexamethasone and DOC, in concentration ranging from 10(-4) to 10(-8) M, were added into the incubation media and incubated 1 and 4 hours. No changes were observed in ANF concentration either in the media or in its tissular concentration as measured by a specific radioimmunoassay. When intact rats were previously treated with DEXA, DOC or DEXA + DOC and their atria incubated "in vitro", an increase in the release of ANF was observed in the Dexa-treated group only, but all treated groups had higher tissular ANF concentration. It is concluded that neither alpha- or beta-adrenergic, nor cholinergic agonists or vasopressin and met-enkephaline stimulate ANF release "in vitro". On the other hand steroids may regulate ANF release and synthesis in the intact rat. It seems likely that the ANF released into the media corresponds to a short peptide.