All the data published for complexation (conditional stability constants and effective ligand concentrations) of trace metals (Cu(II), Zn(II), Pb(II), and Cd(II)) in whole seawater, estuarine and freshwater samples over the past 25 years is compiled and presented in a systematic format. This work is intended as a resource for workers in the field of metal ion speciation in natural waters. The experimental techniques and data interpretation protocols used are briefly discussed, and main problems highlighted.