Up to date Donaggio reaction positive substances derived from serum protein have been shown to be from the α(1)-globulin region, mainly α(1)-AG. One purpose of this study was to purify α(1)-AG from Cohn fraction VI of human serum by means of starch block electrophoresis and to measure the Donaggio titer in it. The other purpose was to compare α(1)-AG with the other protein subfraction. The results were: 1) Pure (about 98%) α(1)-AG was obtained from Cohn fraction VI after heating. The Donaggio titer of α(1)-AG solution was 1.7-2.2/mg/dl. Whole Cohn fraction VI was 1.2, human albumin was 0.7 and α(2)-HS was 0.8. 2) The Donaggio specific activity was indirectly proved to be in the order of α(1)-globulin>α(2)-globulin contained in the Cohn fraction VI. This result supports the previous report.
3) A solution of Cohn fraction VI was almost equal in Donaggio titer per the same concentration of protein to urine after exercise, after treatment by heating at 100℃ for 10 minutes and acidification to pH. 5 by acetic acid. 4) α(1)-AG was concluded to have the highest Donaggio titer of the whole protein subfraction.