This study aimed to optimise the methodology for the use of Corophium insidiosum in a bioassay. Taking into account that it would be suitable to execute the bioassay with organisms having a good sensitivity during the year and low mortality in control sediment, the influence of different temperatures (10-15-20 and 25 degrees C) has been examined. C. insidiosum was collected during August, November 2005 and January 2006, in Mar Piccolo basin (Ionian sea). The results obtained show that this species mortality in the negative control sediment, ranged from 2.6 +/- 0.6% at 10 degrees C in August to 17 +/- 2.2% at 20 degrees C in November, at different temperatures tested. At 20 degrees C there were significant differences in mortality among different months examined. Indeed no relationship among months was found at 15 degrees C. Significant differences between August and November at 25 degrees C, between November and January were not found at 10 degrees C. The 96-h LC50 values found for cadmium at all temperature experimental conditions ranged from 2.11 mg/l (1.57-2.82) to 0.70 mg/l (0.54-0.93). The highest values were found at 10 degrees C in November and January. The results showed that the optimal temperature for the bioassay seems to be between 15 degrees C and 20 degrees C. Even if, at 20 degrees C the mortality differs significantly among organisms sampled.