A binuclear copper(II) complex derived from trimethylamine carboxyborane [tetrakis-mu-(trimethylamine-boranecarboxylato)-bis-(trimethyla mine- carboxyborane)dicopper(II)] was shown to have antineoplastic activity in the Ehrlich ascites carcinoma screen. Metabolic studies demonstrated that the compound suppressed DNA and protein syntheses. The inhibition of DNA synthesis appeared to be due to reduction of the DNA polymerase activity and the regulatory enzymes of de novo purine synthesis. Preliminary data suggest that the compound is an initiation inhibitor of protein synthesis in Ehrlich ascites cells.