This article presents experimental designs focusing on assessing of the bioavailability of metals in aquatic organisms, soil organisms, microorganisms, plants, birds, and mammals. Standardized test systems receive the greatest emphasis. With regard to microorganisms, animals, and plants, the study concentrates on toxicity as an indicator for bioavailability. In respective test procedures, results are usually calculated for total chemical concentrations; chemical analyses are not commonly in routine assessments. For soil organisms chiefly exposed by the water pathway, the bioavailable fraction of contaminants can be roughly determined by chemical analyses in aqueous soil extracts simulating soil pore water concentrations. Human toxicity can be determined using adequate in vitro test designs. In addition to experimental designs, results from the literature dealing with specific problems of bioavailability are presented.