Methods have been developed over the past several decades to measure or predict the accumulation of persistent organic contaminants in plants and animals. Most of these methods determine either the bioconcentration factor (BCF), the bioaccumulation factor (BAF), or the n-octanol/water partition coefficient (Kow). Although BCF and BAF are expensive to determine, they do account for metabolism by the target organism whereas the chemically determined Kow does not. Methods recommended by OECD, ASTM and USEPA for the determination of bioconcentration of chemicals are evaluated. Recently finalized USEPA methods are recommended for the determination of BAF and BCF in fish. The slow-stir method is considered the most accurate for a direct measurement of the n-octanol-water partition coefficient (Kow), but computer estimations of Kow can be used when a direct measurement is unavailable. Recent bilinear equations (Howard et al. 1997) have been derived to predict BCF values from Kow.