Toxicity and antitumor effects of four compounds from the groups of triazoloacridinones and imidazoacridinones were evaluated in transplantable tumor systems in mice, including P388 leukemia, B16 melanoma and 2 colon adenocarcinomas C26 and C38. Tested compounds had moderate antileukemic activity but were active against B16 melanoma and 3 of them were very efficacious against colon tumors, providing high percentages of "cures". Toxicity for healthy mice, as well as antitumor activity, were found to depend on a treatment protocol. The compounds were better tolerated and gave higher antitumor effects when given as fractionated treatment. They displayed also sex-dependent toxicity and activity.