Low-dose Prednisolone probably has a useful role in combination with other drugs, but is ineffective on its own in prophylaxis. Side effects are relatively mild in contrast to high-dose steroids. Azathioprine is a relatively non-toxic drug whose main side-effects are on the bone marrow and liver. As with steroids, it is ineffective on its own. Cyclosporin is undoubtedly the most potent of the currently available immunosuppressives. Careful monitoring is essential to avoid toxicity, in particular nephrotoxicity. Its value is enhanced by relative sparing of suppressor wells and B lymphocytes. While concern still exists regarding progressive long-term nephrotoxicity, it seems now more likely that this can be avoided by careful dose regulation. Hirsutism and cost are two important disadvantages. ALG, ATG and monoclonal antibodies directed against T lymphocytes (eg, OKT3) or surface receptors such as IL-2 receptors are increasingly being used and there is hope of the development of an increasing range of new, more specific monoclonals.