The estuarine fish, spot (Leiostomus xanthurus), was exposed to 0.27, 0.52, 1.01, 1.99, and 3.87 micrograms/liter technical grade heptachlor (65% heptachlor, 22% trans-chlordane, 2% cis-chlordane, 2% nonachlor, and 9% unidentified compounds) for 24 days in a flow-through bioassay, followed by 28 days in heptachlor-free seawater. Concentrations of heptachlor, heptachlor expoxide, and trans- and cis-chlordane in edible tissues were monitored at day 3 and weekly thereafter throughout the bioassay and at the end of the postexposure period. All four chemicals were accumulated by spot. Maximum concentrations of heptachlor were observed on day 3; maximum bioconcentration of the other three compounds were observed on day 17. The average bioconcentration factors for heptachlor and trans-chlordane were 3,600 and 4,600, respectively. Only 10% or less of the maximum concentrations of heptachlor, heptachlor epoxide, and trans-chlordane accumulated during the exposure period remained after 28 days in pesticide-free seawater; an average of 35% of the cis-chlordane remained.