A further development of the coal gasification process will result in an increase of the amount of coal gasification slag (CGS). As yet little is known about the effects of storage in uncovered dumps. If there are any environmental effects, they are most likely caused by accumulation of metals from the CGS or by unacceptable physical properties of the CGS. Growth inhibition, mortality, and metal accumulation were analyzed for the plant Cyperus esculentus and the worm Eisenia fetida on CGS substrate. Pulverized fuel ash (PFA) was used as a reference. Both in the substrate and in tissues the concentrations of the cations Cu, Ni, Pb, and Zn and the anions As, B, Cr, Mo, Sb, and Se were determined. The availability of anions for C. esculentus and for E. fetida is greater in PFA than in CGS. The extent and rate of uptake of anionic metals by the plants is on the whole higher in the wetland situation. The availability of metals, expressed as the concentration factor (CF), in most cases appears to be smaller than 1 for nearly all elements. In E. fetida a CF greater than 1 was found only for the element As, in PFA substrate and 50% CGS. In C. esculentus a CF greater than 1 was found for B and Mo in the PFA substrate as well.