This single-centre study evaluated the adverse effects of anti-thymocyte globulin (ATG) and anti-lymphocyte globulin (ALG) as used for the treatment of aplastic anemia and/or for conditioning regimens prior to stem cell transplantation. ATG/ALG was given to 29 patients a total of 37 times. The incidence of adverse effects was 62.1% (23/37), and fever was the most frequent adverse effect. Therapy was discontinued in only 4 patients (10.8%) due to severe adverse effects. Adverse effects occurred more frequently with ATG (rabbit-derived) than with ALG (horse-derived). Seven patients underwent 2 or 3 cycles of ATG/ALG therapy, for a combined total of 8 times; 6 of those patients (75% (6/8)) experienced adverse effects. Shorter intervals between repeated cycles of therapy appeared to heighten the risk of adverse reactions.