An evaluation of sediment toxicity at Lake Orta, Italy was conducted to compare a toxicity test battery of 6 assays and to evaluate the extent of sediment contamination at various sediment detphs. Lake Orta received excessive loadings of copper and ammonia during the 1900\'s until a large remediation effort was conducted in 1989-90 using lime addition. Since that time, the lake has shown signs of a steady recovery of biological communities. The study results showed acute toxicity still exists in sediments at a depth of 5 cm and greater. Assays that detected the highest levels of toxicity were two whole sediment exposures (7 d) usingHyalella aztecaandCeriodaphnia dubia. The Microtox® assay using pore water was the third most sensitive assay. The Thamnotoxkit, Rotoxkit, Microtox solid phase, and Seed Germination-Root Elongation (pore and solid phase) assays showed occasional to no toxicity. Based on similarity of responses and assay sensitivity, the two most useful assays were theC. dubia(orH. aztecaand Microtox pore water. These assays were effective at describing sediment toxicity in a weight-of-evidence approach.