Since 1988, the State of Maine has monitored dioxin levels in the tissues of predatory and bottom feeding species of fish taken from the state's major water bodies, including five rivers which receive the effluent of bleached kraft paper mills. Data are also available on dioxin concentrations in the effluent of these mills. Monitoring results were analyzed using simple models to yield field bioaccumulation factors (BAFs) for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in Maine rivers. Three BAFs were computed for each fish species at each site to account for declining TCDD levels in mill effluents over time. Mean BAFs (across rivers) ranged from 11,500 to 24,600 for smallmouth bass fillets, from 17,900 to 28,300 for brown trout fillets, from 3000 to 7500 for white perch fillets, and from 78,500 to 106,000 for white sucker whole bodies. Field BAFs obtained in this analysis are similar to factors obtained in recent laboratory studies of TCDD accumulation in fish. Our results suggest that EPA's currently recommended BCF value of 5000 is probably too low. Instead, a value between 15,000 and 25,000 is considered a reasonable estimate of the BAF to use for regulatory purposes in the state of Maine.