Seventeen HIV-1-infected individuals were given AZT (100 mg tid) and ddC (0.375 mg tid) for consecutive periods of four weeks each and for total periods ranging from 8 to 32 weeks (median 17). Thirteen patients were offered AZT/ddC after having received other anti-retroviral combinations containing AZT, whereas in four it was used as front therapy. Before and after AZT/ddC, the median CD4 cell count changed from 184 to 164/uL (p NS), and the median body weight from 60 to 61 kg (p NS). Increases in hematological parameters were observed in patients previously exposed to AZT. In eight patients the side effects of AZT (gastrointestinal intolerance, cephalalgia and fever) disappeared when switched to ddC, whereas in one a reversible peripheral neuropathy ensued. The dosages of AZT/ddC used in this trial were well tolerated.