In a randomized study, the effect of single agent therapy, with CCNU was compared with that of BCNU in previously treated patients with advanced Hodgkin's disease. The dosage of CCNU was 100 mg/m2 p.o. q. 6 weeks and of BCNU, 200 mg/m2, p. 6 weeks with dose modification adjusted to individual tolerance. For 60 evaluable patients the response rate (complete and partial was 60 for CCNU and 28% for BCNU (p = 0.025); median duration of response was 4.5 months and 2.0 months, respectively (P = 0.26). Median survival for responders was 11.0 months and for non-responders 5.0 months. No major difference was observed in hematologic toxicity between the two compounds. Used as single agents in equitoxic dosages, CCNU is superior to BCNU for the treatment of previously treated advanced Hodgkin's disease, and CCNU has the additional advantage of oral administration.