Young and adult uninephrectomized male rats (aged 25 and 87 days respectively) were exposed to an increased salt intake (1% saline as the only drinking fluid) either alone or in combination with DOCA-treatment for 25 and 46 days respectively. Age dependent differences of interrelationships between saline intake (SI), blood pressure (BP) and kidney weight (KW) were studied during development of salt and DOCA-salt hypertension to specify possible factors involved in the higher susceptibility of the young rats to these regimes. Correlation analysis was employed using the step-wise regression procedure. Only in the young rats did saline treatment induce an increase in KW, which preceded the development of mild hypertension. This age group also responded to DOCA-saline treatment with a more pronounced increase in both BP and KW. SI was higher in the young than adult rats exposed to either saline or DOCA-saline treatment. This, however, does not account by itself for the higher hypertensive response of the young rats, since there was no primary relationship between SI and BP in the hypertensive groups. Increase in KW accompanying development of hypertension was dependent on BP in the young rats and on SI in adult rats. This indicates that saline and DOCA-saline treatment renders the kidneys of young rats more sensitive to damaging effects of BP, which play a part in the more pronounced hypertensive response.