THE NITROSOUREAS (BCNU, CCNU, methyl CCNU) represent a new class of antineoplastic agents with a broad spectrum of antitumor activity. They are cell-cycle nonspecific cytotoxic agents. Postulated modes of action and pharmacology of these nitrosoureas are reviewed. Their therapeutic effectiveness as single agents and in combinations have been recognized in malignant lymphomas, multiple myeloma, melanoma, glioblastoma multiforme, gastric and colorectal carcinoma, and small-cell carcinoma of the lung. The nitrosoureas are administered on an intermittent (6–8-week schedule because of delayed and frequently severe bone marrow toxicity which may be cumulative in nature.