Two new methods are presented here which allow a sensitive determination of chlorine, chloramine, chlorine dioxide, chlorite and chlorate. Chlorine, chloramine and chlorine dioxide are analyzed by a colorimetric method using the reagent ABTS (2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonate) without interference from each other. The chlorine species oxidize ABTS to the green colored radical cation ABTS, which has absorbance maxima at several wavelengths, for example at 405 or 728 nm. Chloramine is measured selectively after reaction of chlorine and chlorine dioxide with nitrite. Chlorine dioxide is measured selectively after masking chlorine with glycine in the presence of mercury(II). A detection limit for the three species of about 5 ug/L is achieved. The advantage of using ABTS over DPD is the much higher stability of the colored product and the easy distinction between chlorine, chloramine and chlorine dioxide. ABTS allows the use of 405 nm as detection wavelength, which is found in portable photometers. The method is therefore suitable for field measurements. Includes 39 references, table, figures.