The use of "Sediment-Chromotest" for monitoring biodegradation processes is based upon its sensitivity to detect organics, inorganics, and toxic heavy metals commonly found in oily sludges. These residues, treated by bioaugmentation, were evaluated for toxicity by carefully monitoring experimental plots before the biodegradation process, during its development, and then for a period of 200 days of treatment. The data obtained demonstrated that the sediment biodetoxification process presented a point of maximum toxicity at the end of the first phase (53 days) due to the generation of intermediate metabolite products from the breakdown of complex compounds. Following the first phase, as intermediate metabolites disappeared, toxicity becomes almost negligible after a 200 day period. © 1996 by John Wiley & Sons, Inc.