The tissue renin-angiotensin systems (RAS) may have specific roles that complement those of the systemic RAS. In the adrenal, the tissue RAS has been implicated in the regulation of glomerulosa tissue growth and function, and in mediating the response of the tissue to stimulation by ACTH and potassium ions. To examine the role of the rat adrenal tissue RAS in its response to angiotensin II stimulation, adrenals were incubated either as bisected glands or as separated capsular glands (largely glomerulosa) under control conditions, or in the presence of the angiotensin-converting enzyme inhibitor captopril, or of angiotensin II, or both. Captopril inhibited the two different tissue preparations in different ways. In the capsular gland it inhibited basal aldosterone output, but facilitated its response to angiotensin II. In the bisected gland, captopril inhibited the response of aldosterone to angiotensin II. Other data suggest that one way in which captopril functions is by preventing the conversion of fasciculata-generated 18-hydroxydeoxycorticosterone (18-OH-DOC) to aldosterone in the glomerulosa. Immunolocalisation of 18-OH-DOC in perfused rat adrenal confirms that one function of angiotensin II is to mobilise tissue-sequestered 18-OH-DOC. The results illustrate the importance of tissue RAS in the synthesis of aldosterone and the response to angiotensin II.