In vitro data suggest that there are complex pathways of angiotensin production and that multiple receptor subtypes mediate the actions of this peptide. These observations may have important in vivo physiological and pharmacological implications. This paper reviews the current state of knowledge of angiotensin II (Ang II) biosynthetic pathways and the molecular biology of angiotensin receptors. The similarities and differences between inhibiting angiotensin-converting enzyme activity and blocking Ang II receptors with regard to their clinical application in the treatment of hypertension are discussed.