The experiment with sodium chloride demonstrates the importance of carefully evaluating weak mutagenic responses observed with high concentrations of test compounds. The positive mutagenicity is likely not due to a direct interaction with DNA but from some indirect mechanism resulting from the extremely nonphysiological condition of the test. A 'blind testing scheme' might conclude that sodium chloride should be tested in the rodent bioassay. For short-term tests to be useful, all results must be carefully analyzed and evaluated using all available information including the likelihood that the test conditions may impact the outcome. To do otherwise compromises the utility of the particular test systems.