Primary aldosteronism (PA) is a common form of secondary hypertension with an international prevalence rates between 5 and 10 %. It is characterized by a high autonomous aldosterone production that causes cardiovascular damage, renin suppression, hypertension, sodium retention, potassium excretion and hypokalemia. The screening of PA is a simple test measuring aldosterone to renin ratio (ARR) with immunoassay method. This test is currently considered as the most reliable screening tool for PA.     The main objective of the study was to evaluate an ELISA-method, for detection of aldosterone and renin in blood plasma, to be used for routine analysis in the laboratory. The second aim was to investigate the effect of refreezing samples, considering that cryoactivation of prorenin might occur.     One hundred blood samples were analysed, in regard to aldosterone and renin, by using two commercial ELISA assays (DRG ELISA from DRG Diagnostics, Germany) on a Dynex DS2 instrument. In addition, the accuracy and precision of the methods were calculated. The effect of refreezing was investigated with a series of eight samples, which were analyzed twice on the same instrument.     Both assays performed well. The resulting data showed good precision and accuracy. The correlation between the original and refreezed samples was good, r = 0.989 and r = 1.0 for aldosterone and renin respectively. Considering that the study only included eight samples, further investigation is recommended.     Evaluation showed that both immunoassays are reliable in diagnostic use and the ELISA-method is suitable to implement in the laboratory for routine analysis.