Exciting new research in the field of oxidant by-products in drinking water and wastewater is progressing along three main lines: (1) investigation into the mechanism of the aquatic humic/aqueous chlorine reaction; (2) correlation of by-product identity and yield with mutagenic activity; and (3) analysis of previously intractable organic by-products such as high molecular weight polar substances and N-chloroorganic compounds. Just as earlier research was stimulated by the development of the combined gas chromatograph/mass spectrometer, these new investigations have been fostered by the development of new analytical methods such as solid state C-13 nuclear magnetic resonance spectroscopy, extended mass range mass spectrometry, new ionization techniques such as fast atom bombardment and combined liquid chromatography/mass spectrometry. Application of these new techniques is allowing these and many other important public health questions to be addressed. (Copyright (c) 1985 Elsevier Science Publishers B.V.)