Although alternative therapy for PCP remains limited, the role of TMP/SMX desensitization becomes increasingly important in patients with AIDS. Various successful desensitization protocols have been described in this article. As there are no established guidelines, it appears that the desensitization procedure can occur in small successive doses given each day or one small dose given daily. An evaluation of the severity of allergic reaction can be used to determine the type of dosing regimen. We believe that protocols starting with low doses and slow titration to full-dose therapy, as used at our institution, should be efficacious. Monitoring of the patient after the desensitization procedure should continue, as sensitivity may reoccur. In addition, while the patient is undergoing desensitization, some investigators recommend that alternative therapy be continued until full-dose TMP/SMX therapy is achieved. Also, it is important to realize that once a patient is successfully desensitized, medication compliance must be maintained because, theoretically, reexposure to the drug after a lapse in therapy may result in hypersensitivity reactions. Therefore, this procedure and the possibility of serious adverse effects, such as Stevens-Johnson syndrome and anaphylaxis, should be evaluated carefully and discussed thoroughly with each patient prior to initiation of therapy. Finally, a study of sufficient size should be performed to evaluate the efficacy of desensitization regimens and establish specific dosing guidelines.