To determine the dangerous blood group ‘O’ donors o reoccurrence at the Federal Teaching Hospital, Abakaliki. One hundred (100) cell grouped and sero-typed blood group ‘0’ donors (94 males and 6 females) aged 18 and 45 years participated in this study between February and September 2007 at the Blood Bank(phlebotomy) section of the Teaching Hospital, Abakaliki after an informed consent. The presence of both the alpha (∝) and beta (β) haemolysin were determined using donors sera for reverse grouping. Haemolysin indicates the presence of haernolysis which is in the sera of the dangerous blood group ‘O’ donors. The study discovered that 36 male donors out of 100 donors studied were positive to haemolysin. This result was statistically analyzed using student’s t- test at 95% confidence interval with P value of 0.05. The numbers of haemolysin positive donors were significantly increased in comparison with the heamolysin negative donors (P< 0.05). This result pattern suggests a relatively high level of blood transfusion reactions in this part of the world. Screening test for dangerous group ‘O’ donors should be carried out routinely in blood transfusion laboratories to order to reduce the occurence of blood transfusion.