A national interlaboratory study to validate two alternative methods to the Draize rabbit's eye test, co-ordinated by ZEBET at the German Federal Health Office (BGA), is described. The aim of the study is to classify chemicals according to their irritation potential using the neutral red/kenacid blue (NR/KB) cytotoxicity assay and the hen's egg chorioallantoic membrane (HET-CAM) test. During the last two years 12 toxicology laboratories from industry, universities and other research institutions have tested 32 substances from a variety of chemical classes, characterized by a broad spectrum of locally irritating properties, using the NR/KB cytotoxicity test and the HET-CAM assay. Intra- and interlaboratory reproducibility of the two methods was investigated under standardized conditions. The so-far limited evaluation of the interlaboratory assessment phase of validation indicates that the results of the Draize rabbit's eye test correlate better with the results of the HET-CAM test than with those of the cytotoxicity test as far as false negative results are concerned. However, the intra- and interlaboratory reproducibility of the cytoxicity test is better than that of the HET-CAM test. The validation project has recently entered the stage of database development during which 150 chemicals will be tested in seven laboratories to provide information on whether and to what extent the NR/KB test and the HET-CAM test can replace the Draize rabbit's eye test for the classification and labelling of chemicals with regard to their eye irritation potential.