The development of hypertension in two-kidney, one clip renal hypertensive rats (2K, 1C RHR) was not altered by treatment with DOCA and saline solution as drinking fluid for two months of observation. However, the administration of DOCA and salt suppressed plasma renin activity (PRA), the renal renin content (RRC) of the clipped kidney and the response to a single oral dose of captopril (10 mg/kg). The weight of the contralateral kidney was increased by the administration of DOCA-salt, while that of the ischaemic kidney was not changed.The withdrawal of DOCA-salt treatment restored the PRA and the effects of captopril to a similar degree to the non-treated group. The acute hypotensive effects of captopril were reduced on the 10th week compared with the 7th week after renal arterial constriction in 2K, 1C RHR. The fall in blood pressure induced by captopril significantly correlated with the initial PRA both in the 7th and 10th week after clipping. There was a significant correlation between PRA and RRC of the clipped kidney.Rats previously treated with DOC-salt had either removal of the contralateral kidney with removal of the clip from the ischaemic kidney, or removal of the ischaemic kidney. Blood pressure fell to normal levels in the undipped group and in the nephrectomy group, but the fall in the latter group was transient and within two weeks had risen to significantly higher levels than in the undipped group.It is concluded that structural vascular change following DOC-salt hypertension is insufficient to cause persisting hypertension except when it occurs in the renal circulation.