The effect of methyl substitution on the biological properties of the ellipticines was reexamined. 9-Hydroxy-6H-pyrido[4,3-b]carbazole was synthesized and shown to be devoid of antitumor activity in murine P388 lymphocytic leukemia in mice. 5-(Hydroxymethyl)-11-methyl-6H-pyrido[4,3-b]carbazole (46) and its N-methylcarbamate (48) were synthesized and their effect on macromolecular synthesis in HeLa cells and their antitumor properties were compared with those of ellipticine. In contrast to the alkaloid 1 and the hydroxymethyl derivative 46, which produced partially reversible inhibition of [3H]thymidine incorporation, the carbamate ester irreversibly blocked incorporation of the tritiated pyrimidine. The ester was also a more potent antitumor agent in P388 lymphocytic leukemia than 1 or 46.