A cytotoxicity test with the crystal violet staining method was developed using Chinese hamster lung and HeLa S3 cells in 96-well microtitre plates with an automatic plate reader, to facilitate examination of serial dilutions of the test substance. A good correlation was observed between this procedure and routine cell counting. However, for some chemicals results of the microtitre plate method differed from colony formation counts, particularly when the chemical induced cell stasis. In an application of the microtitre cytotoxicity assay to injection drugs, some drugs that are widely used proved to be very cytotoxic.