The report summarizes the results of an interlaboratory comparison for bioconcentration (BCF) testing using the eastern oyster (Crassostrea virginica) and the organic chemicals pentachlorophenol (PCP), 1,2,4-trichlorobenzene (TCB), and p, p'-DDE. The means BCFs and high to low BCF ratios (H/L ratio) for PCP, TCB and p,p'-DDE were 64 (2.4), 168 (2.3) and 52,600 (3.4), respectively. The test method (ASTM Draft 9) used for all three chemicals and four participating laboratories resulted in data with a mean high to low ratio of 2.7, which represents the extreme estimate of variability. The mean H/L ratios for the time to 90% depuration for all three chemicals was 3.3. Considering the varying degrees of experience between participants in conducting BCF tests, the wide geographic distribution between participants, and the different dilution water characteristics, the results were very reproducible.