Combination chemotherapy regimens achieve complete remissions in 60% to 80% of patients with non-Hodgkin's lymphomas; however, the majority of patients will relapse, and resistant disease remains a problem. Attempts to identify new, effective chemotherapy agents have primarily focused on the development of analogues that, unfortunately, have uniformly failed to provide a substantial therapeutic advantage. Drugs with a unique mechanism of action are more likely to be successful; among these are the purine analogues (e.g., fludarabine, 2'-deoxycoformycin, 2-chlorodeoxyadenosine) and agents that can reverse clinical drug resistance. The number of patients who can be cured can be increased only by incorporating new agents into front-line regimens through carefully designed clinical trials.