Infrared, solid-state13C NMR and liquid-state1H NMR spectra were recorded as a means of investigating structural components in the high-molecular part of pulp mill effluent and different stages of the chlorine bleaching process. Comparison was made with the spectra of kraft lignin, native lignin, and humic substances. The1H and13C spectra of mill sample fractions showed that there are no marked differences in the structure of high-molecular-weight fractions before and after the purification plant. However, comparison of the13C spectra of mill samples with the spectra of native and kraft lignin showed that lignin undergoes a pronounced change in the bleaching process. The13C NMR spectrum of the purification plant outflow sample closely resembled the spectra of the humic reference materials. The most significant difference in the infrared spectra of the chlorolignin fractions and reference humic materials was the presence of strong C—CI absorption bands in the chlorolignin spectra and their absence from the spectra of humic samples.