This report describes a method for cytotoxicity screening of biomaterials based on colony formation of V 79 cells For this test, two metals (titanium and nickel), two ceramics (alumina ceramic and tricalcium phosphate), and two types of polymeric material lhigh density polyethylene (HDP) and polyvinylchloride (PVC)l were used Each metal and ceramic was cast into a disk and semidisk 49 mm in diameter and 1 to 2 mm thick The HDP was molded into a petri dish and PVC was used as a thin film The materials were sterilized by heating or with ethylene oxide and placed in plastic petri dishes, after which 8 ml cell suspension containing 100 cells were added to each dish After 1 week, the colonies formed on the materials were fixed, stained, and then the number of colonies was counted Titanium, alumina ceramic, and HDP showed no differences from the controls in terms of colonies On the disks and the semidisks of nickel and tricalcium phosphate and on the thin disks of PVC, however, no colonies were detected The V 79 cells used in this experiment showed a rapid and logarithmically stable growth curve and such a high rate of colony formation as to form visible noticeable colonies, and were therefore suitable cells for screening test the cytotoxicity of biomaterials Unlike other previously reported methods of in vitro cytotoxicity testing, this method permits assay of colonies formed from a single cell after proliferation directly on the materials Moreover, the test with semidisks permits simple screening to assess the cytotoxicity is caused by either the chemical substances or the physical properties of the materials Furthermore, since colonies of V 79 cells are formed even on metals, it is generally easy to evaluate quantitatively the cytotoxicity of solid materials As it has more advantages than other methods, this screening method appears suitable for the cytotoxicity test of biomaterials.