Contrary to a recent suggestion, new and useful drugs for the treatment of human cancer continue to be developed although clinical trials today are more difficult and the chances for success are diminished. In the past, research at Southern Research Institute led to the development of two new classes of clinically useful anticancer agents, the nitrosoureas and the imidazole triazines. More recently, we have developed an interesting family of cytotoxic compounds, the haloadenine nucleosides, that are resistant to deamination and show biological activity comparable to the corresponding adenine nucleosides given in combination with 2'-deoxycoformycin, a potent inhibitor of adenosine deaminase. Among them, the 2-haloadenine arabinonucleosides and 2'-deoxyribonucleosides appear to have the necessary selectivity for neoplastic cells to be useful anticancer agents.