Human (pro)renin receptor ((P)RR) has been implicated in the augmentation of many biological and cellular processes through bindings to its ligands, renin and prorenin. In this study, we investigated the effects of aliskiren, a direct oral renin inhibitor, on the activities of free and (P)RR-bound forms of human mature renin. We also elucidated the effect of aliskiren on the 'renin activity' of the receptor-bound form of prorenin. Aliskiren had an IC(50) of 0.72 nmol l(-1) against renin. The compound competitively inhibited renin activity with an inhibitory constant (K(i)) of 0.18 nmol l(-1). Furthermore, the dissociation constants (K(D)) for aliskiren from renin and prorenin bound to (P)RR were determined using surface plasmon resonance in a BIAcore assay system (Uppsala, Sweden). These values were estimated to be 0.46+/-0.03 and 0.25+/-0.01 nmol l(-1), respectively. The compound competitively inhibited the renin activities of (P)RR-bound forms of both renin and prorenin with a K(i) of 0.14 and 0.15 nmol l(-1), respectively. These results indicate that aliskiren could be a potent inhibitor of the free forms of mature renin and of the receptor-bound forms of renin and prorenin.Hypertension Research advance online publication, 22 July 2010; doi:10.1038/hr.2010.136.