Over the last two years, the laboratory and others have identified mono-, di-, and trichloro- acetic acids as major byproducts of drinking water disinfection. In areas of the country where relatively high levels of bromine ion are naturally present in the source water, it is expected that significant amounts of the corresponding bromo and mixed chloro-bromo acetic acids will be formed. While developing an automated GC/MS procedure to 'screen' for both previously identified disinfection byproducts as well as the haloacetic acids it was discovered that reference mass spectra for 4 of the 9 possible chloro/bromo acetic acids (as their methyl esters) were unavailable. The paper presents experimental reference spectra for the methyl esters of the four acids mentioned above. All nine acids were synthesized in-situ by reacting an aqueous solution of phenol with chlorine in the presence of various amounts of bromide ion.