A number of methods for determining the general toxic effects of test chemicals on cells in culture are now at the validation stage. Three such methods based on measurement of total cell protein or neutral red uptake and on the detection of morphological effects have been compared. The cell line used was 3T3-L1 (a continuous fibroblast cell line derived from mouse embryos). The results obtained in a blind trial with 30 coded chemicals indicated a close correlation between the relative cytotoxicities of chemicals tested by all three methods.