Hexachlorobenzene (HCB) is a persistent environmental pollutant that bioaccumulates in tissues of marine and fresh water fish. Once taken up by these tissues, biodegradation is very slow with pentachlorophenol and polar conjugates as possible metabolites in aquatic organisms. Numerous studies have been done on HCB uptake and depuration in fish. In these studies the HCB bioconcentration factors (BCFs) varied from 5000 to 40,000 (wet weight basis) with half-lives (t 1/2) from a few days to several years. Although several studies have examined HCB uptake in invertebrates, only Oliver's (1987) study estimate a BCF. Oliver (1987) found that the BCF of HCB in oligochaete worms was 3120 when calculated on a wet weight basis, with a t(1/2) of 27 days. However, in Oliver's study the worms were buried in the contaminated sediment and the BCF calculated using the interstitial water concentration. As a portion of the HCB body burden was likely due to the ingestion of particulates, the reported BCF value may be in error.