The objective of the study was to determine the effects of sediment from various sediment core depths on survival and weight gain of larvae of the dipteran midge, Chironomus tentans, during 10-d laboratory exposures. Sediment cores were collected from 12 sites in the Trenton Channel of the Detroit River in 1987 and sectioned into 5-cm intervals to a depth of 25 cm. Percent reductions in larval weight gain, relative to that in control sediment, were calculated for each interval. Two sites were classified as very toxic, three sites as toxic, three sites as slightly toxic, and four sites as good quality benthic habitat. The utility of sediment core toxicity profiling and the C. tentans bioassay for three-dimensional sediment quality assessment are discussed, as well as comparisons between the results of laboratory assays and field surveys of benthic macroinvertebrates. The assay results are used to estimate the volume of toxic sediment at eight sites and determine the costs of dredging and disposal of the toxic sediments. Preliminary estimates of remedial actions were developed to achieve several levels of mitigation of the toxicity of sediment to macrozoobenthic populations in the Trenton Channel.