Vverification of laboratory bioassay results in the field is a complex process which is currently being tested in a range of freshwater and marine habitats by the Florida State University Aquatic Study Group. Verification studies range from single-species bioassays to multispecies microcosms of soft-sediment benthic macroinvertebrates. The basic question involves whether laboratory results can be reasonably extrapolated to field conditions. The chief factors which complicate direct extrapolation include physical-chemical habitat features, reproduction and recruitment of populations, immigration-emigration, predation, and competition. Statistical models are being developed to test the comparability of laboratory and field data in the estimation of the effects of toxic substances on natural aquatic systems.