Sediment toxicity tests compared chronic effects on survival, growth, and biomass of juvenile freshwater mussels (28-d exposures with Lampsilis siliquoidea) to responses of standard test organisms, amphipods (28-d exposures with Hyalella azteca) and midges (10-d exposures with Chironomus dilutus), in sediments from two lead-zinc mining areas: Tri-State mining district and Southeast Missouri (SEMO) mining district. Mussel tests were conducted in sediments sieved to <0.25 mm to facilitate recovery of juvenile mussels (2 to 4 mo. old). Sediments were contaminated primarily with lead, zinc, and cadmium, with greater zinc and cadmium concentrations in Tri-State sediments and greater lead concentrations in SEMO sediments. The frequency of highly toxic responses (reduced 10% or more relative to reference sites) in Tri-State sediments was greatest for amphipod survival (25% of samples), midge biomass (20%), and mussel survival (14%). In SEMO sediments, the frequency of highly toxic samples was greatest for mussel biomass (25%) and amphipod biomass (13%). Thresholds for metal toxicity to mussels, expressed as hazard quotients based on probable effect concentrations, were lower for SEMO sediments than for Tri-State sediments. SEMO sites with toxic sediments had 2 or fewer live mussel taxa in a concurrent mussel population survey, compared to 7-26 taxa at reference sites. These results demonstrate that sediment toxicity tests with juvenile mussels can be reliably conducted using modifications of existing standard methods; that the sensitivity of mussels to metals can be similar to or greater than standard test organisms; and that responses of mussels in laboratory toxicity tests are consistent with effects on wild mussel populations. This article is protected by copyright. All rights reserved.