Crude solvent extracts were prepared from three sediment sites in Ireland namely Bull Lagoon, Dunmore East and Dublin Port. These were assayed with Tisbe battagliai and the Microtox ® system. The extracts were chemically characterised using a variety of analytical techniques for a suite of organic contaminants. Metals and organic contaminant concentration data are reported for the three sites. On the basis of determined toxicity and chemical analysis of these crude extracts, a further bioassay-directed fractionation (BDF) employing the Dunmore East crude organic extract was conducted in addition to chemical analysis. For the crude extracts, T. battagliai and Microtox ® system demonstrated an order of decreasing toxicity for each of the three sites to be Dublin Port > Dunmore East > Bull Lagoon. Microtox ® system EC 10 values after 30 min exposure were 1.08%, 11.6% and 26.9% solvent extract for these sites, respectively. Fractionation of the Dunmore East extract revealed that fraction 1 was the most toxic fraction to both the T. battagliai and the Microtox ® system demonstrating EC 50’s after 48 h and 30 min of 44.7% and 16.8% solvent extract for the T. battagliai and Microtox ® assays, respectively. T. battagliai however did show increased sensitivity to fraction 3 when comparing EC 10 values and demonstrated an EC 10 value of 17.8% solvent extract after 48 h. Fraction 1 was shown to contain the highest quantity of the butyltins, in particular TBT in relation to fractions 2 and 3. A useful BDF technique was developed and employed in this study.