Besides general complications of immunosuppression such as increased susceptibility to opportunistic infections or malignancy, individual immunosuppressive agents are associated with specific side effects. Nephrotoxicity is the major side effect of cyclosporine (CsA). Various attempts have been made to minimize this toxicity, such as monitoring drug blood levels, modifying the protocol, and coadministering other agents. Other side effects caused by CsA are hepatotoxicity, hyperkalemia, hypertension, tremor, gum overgrowth, and hirsutism. Azathioprine (AZA) causes dose-related bone marrow suppression, commonly leading to leukopenia. Careful monitoring of complete blood cell count and dosage adjustment according to white blood cell count are usually adequate to prevent serious leukopenia. The side effects of corticosteroids are numerous and include slow wound healing and de novo insulin-dependent diabetes mellitus. Many complications are dose related, and with low dosage or discontinuation of steroids, their frequency rapidly decreases. Antilymphoblast and antithymocyte globulins (P-ALG) are foreign antibodies and may cause allergic-type reactions such as fever, chill, and hypotension. The initial side effect of monoclonal antibody (muromonab-CD3, OKT3) is similar to that of P-ALG. It includes high fever, shaking chills, headache, rigors, and hypotension. To prevent it, acetaminophen, an antihistamine, and a steroid usually are administered before injection. Because this agent is also associated with high frequency of pulmonary edema, it should not be given to any patient who has more than 3% body weight gain during the week prior to therapy. In rare case, it causes aseptic meningitis or encephalopathy, which is manifested by fever, severe headache, and seizure.