Blood pressure was measured indirectly (using the tail-cuff method) and intra-arterially in conscious rats following one of three experimental procedures carried out in order to determine which resulted in the most marked and reproducible form of adrenal regeneration hypertension (ARH). All rats were unilaterally adrenalectomized and given NaCI solution (1%). In some rats, the remaining adrenal gland was either enucleated (AE rats) or compressed (AC rats) but both kidneys were left intact. During the fourth week after surgery, indirectly measured systolic blood pressure was higher in AE and AC rats than in sham-operated (SO) rats but, when measured intra-arterially, the magnitude of the developed hypertension was small (AC rats) or was absent altogether (AE rats). However, when a kidney was removed at the time of enucleation (AEN rats), the levels of systolic blood pressure, measured indirectly or intra-arterially, were markedly and consistently higher than in the corresponding group of uninephrecto-mized SO rats. The magnitude of the developed hypertension was similar in mature male and immature female AEN rats. We conclude that mature male rats, unilaterally nephro-adrenalectomized and given NaCI solution (1 %), provide a marked and reproducible model of ARH.