Ethylene glycol ethers, their aldehyde and their acid metabolites were evaluated for their mutagenicity with the Ames test. The Salmonella typhimurium his- tester strains TA 97a, TA 98, TA 100 and TA 102 were used with and without rat S9 mix. Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol n-butyl ether and their corresponding aldehyde and acid derivatives were tested up to 10(-4) mol/plate (around 10 mg/plate) or up to cytotoxic concentrations. All tested substances gave negative results with TA 98, TA 100 and TA 102 either with or without S9 mix. In contrast, ethylene glycol n-butyl ether (EGBE) and the aldehyde metabolite of ethylene glycol monomethyl ether, methoxyacetaldehyde (MALD), displayed mutagenic potency in strain TA 97a with and without S9 mix at high concentrations. A significant number of revertants was obtained from 19 mumol/plate EGBE (2.2 mg/plate) and from 34 mumol/plate MALD (2.5 mg/plate). At these concentrations the level of revertants reached up to 7-fold and 3-fold the control values for EGBE and MALD respectively.