We measured plasma aldosterone levels to determine whether or not the values obtained reflect the severity of cerebral stroke. All 36 patients with cerebral stroke studied were diagnosed with CT & MRI, and they were classified into 3 groups according to the Glasgow coma scale(GCS)-mild(GCS 14-15), moderate(GCS 9-13) and severe(GCS<8) group, and control of 10 patients, who were scheduled for elective lumbar laminectomy. Blood samples were taken on admission, the 3rd, and 7th hospital day. Aldosterone was measured by radioimmunoassay(normal values : below 150pg/ml). The results obtained were as follows ; 1) Aldosterone levels in control group(n=10) were 128pg/ml(SD+/-21) on admission, 109pg/ml(SD+/-4) on the 3rd day and 102pg/ml(SD+/-18) on the 7th day after admission. 2) Aldosterone levels in mild group(n=12) were 137.0pg/ml(SD+/-137.4) on admission, 107.5pg/ml(SD+/-89.9) on the 3rd day and 64.4pg/ml(SD+/-65.4) on the 7th day after admission. 3) Aldosterone levels in moderate group(n=6) were 195.1pg/ml(SD+/-159.1) on admission, 153.1pg/ml(SD+/-116.3) on the 3rd day and 85.7pg/ml(SD+/-53.0) on the 7th day after admission. 4) Aldosterone levels in severe group(n=18) were 230.3pg/ml(SD+/-107.3) on admission, 219.7pg/ml(SD+/-135.8) on the 3rd day and 267pg/ml(SD+/-233) on the 7th day after admission. The results of this study indicate that aldosterone levels on admission, the 3rd, and 7th day were significantly higher in severe group than in control group and aldosterone may be useful as biochemical markers in the acute stage of cerebral stroke, especially in severe group.