Structure and biomass of two sets of benthic test systems--one colonized in the laboratory, the other on an estuarine bottom--were compared to structure and biomass of a community from a natural estuarine bottom. According to cluster analysis of the species from each system, the laboratory-colonized samples were most different from the other groups (60% dissimilarity level) whereas field-colonized and natural-bottom groups were more similar (40% dissimilarity level). Total density and biomass were greatest in the field-colonized samples, and least in the laboratory group. However, size of individuals of dominant fauna showed that the natural bottom supported more biomass per individual than the field-colonized group. The authors concluded that if sediment boxes were to be used to mimic the natural benthos, then the best experimental approach was to employ sediment boxes colonized in the field contrasted to boxes colonized in the laboratory.