The reverse transcriptase inhibitor 2',3'-dideoxycytidine (ddC) is capable of mediating virologic and immunologic improvements in some patients with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex. However, severe peripheral neuropathy often develops as a dose-limiting toxicity in ddC-treated patients. Lower doses of ddC may avoid this side effect, while retaining antiviral activity associated with this drug. A series of clinical trials is currently examining regimens employing simultaneous or alternating administration of ddC and 3'-azido-3'-deoxythymidine (zidovudine). Concurrent therapy with more than one drug may allow the use of decreased drug doses and thus reduce dose-dependent toxicities, whereas alternating schedules would provide rest periods from each drug without interrupting therapy. Since zidovudine and ddC possess different toxicity profiles and zidovudine-resistant strains remain susceptible to ddC in vitro, such regimens could theoretically provide additional benefits and reduced toxicity, compared with either agent administered alone. It is hoped that these ongoing and future studies will uncover new and better ways to exploit the therapeutic potential of ddC. However, at present, ddC is an experimental drug and should not be used outside the setting of an approved clinical protocol.