For a broad range of circumstances, we show that reliable bioconcentration factor (BCF) estimates can be made using a study design that is based on standard regulatory guideline test procedures but that uses significantly fewer animals and resources. This minimized design involves taking tissue samples only twice during a 14-d depuration period. The utility of the minimized test design was first assessed by resampling data from a series of standard guideline tests and calculating the BCF estimates that would have been obtained if the test had been performed using the minimized design. Data from 25 bioconcentration curves giving BCF estimates ranging from approximately 0.3 to over 20,000 were used. The correlation of log BCF estimates from the guideline study with log BCF estimates from the simulated minimized tests was r=0.99, and the slope of the regression line was 0.96. The robustness of BCF estimates to random variation in measurement of chemicals in fish and water (coefficients of variation of concentrations ranging up to 25%) was evaluated using Monte Carlo simulations. For chemicals with depuration half-lives of less than the length of the depuration period, median BCF estimates from the Monte Carlo simulations of the minimized design were always within 7% of the true BCE The ratio of the 95th to the 5th percentile BCF estimates was always less than or equal to 3.7. Furthermore, the span from the 95th to the 5th percentile of BCF estimates was only 15% wider in the minimized test than in the full guideline test, even though animal use and analytical effort was markedly reduced.