In vivo cell growth inhibition of Ehrlich ascites carcinoma (EAC) has been evaluated with chloroacetohydroxamic acid, (CHA), having -CH2 Cl, for the -NH2 group of hydroxyurea (HU). The inhibitory character of CHA against EAC in mice model has been found to be comparable with that of HU. Cell growth inhibition by CHA is accompanied by inhibitions of DNA and protein synthesis of the treated cells. The transplantability of EAC cells treated with a single dose of (100 mg/kg) CHA is found to be reduced. Enhanced intraperitoneal macrophage is observed in normal mice following CHA (100 mg/kg) treatment. Deviations of hematological parameters and alkaline phosphatase (ALKP) activity consequent to tumor growth are found to be recovered in tumor bearing mice treated with CHA. All these studies suggest the importance of CHA for further trial as a potent antitumor agent.