AbstractWhole body accumulation and tissue distribution of dieldrin in rainbow trout were studied through oral‐dose disposition tests and subchronic exposures via water (0.04 and 0.08 μg dieldrin/L) and/or diet (0.087 μg dieldrin/g fish/d). Growth and no‐growth (maintenance) rations of 4 and 2% body weight per day were employed. In subchronic tests, apparent steady‐state residue concentrations depended on ration and exposure concentration after 8 weeks of exposure. At 16 weeks, mean whole fish residue concentrations ranged from 120 to 1,400 ng dieldrin/g fish. Combination food and water exposures at a growth ration produced the highest accumulation values (1,300–1,400 ng dieldrin/g fish). Maintenance rations apparently limited accumulation to a maximum of 360 ng dieldrin/g fish. Whole body dieldrin concentration, calculated on the basis of total lipids, greatly reduced the differences in residue levels due to ration.Tissue distribution of a single oral dose of [14C]dieldrin was determined in naive (no pretreatment) fish and those preexposed via the diet for 2, 4 or 6 weeks. Tissue concentrations of the tracer dose were determined 48 h following administration. Retention of the [14C]dieldrin was similar in most tissues of naive, 2‐ or 6‐week dieldrin‐pretreated fish with a slight downward trend with duration of pretreatment. Retention of14C in the bile of fish receiving maintenance and growth treatments increased two‐ and five‐fold, respectively, in 6‐week pretreated as compared with naive fish. After 4 weeks of pretreatment,14C concentrations peaked in all tissues except the bile,