Induction of the cytochrome P4501A (CYP1A) enzyme system in fish is a common biomarker of exposure to aromatic hydrocarbons. Induction of CYP1A can be measured at a number of steps in the transcription—translation—functional protein pathway using a variety of techniques. The present study examined the range of these measurements from 94 published papers in an attempt to examine the statistical characteristics of each method. Cytochrome P4501A induction, as measured by catalytic ethoxyresorufin-O-deethylase (EROD) activity, protein levels (enzyme-linked immunosorbent assay, Western blot analysis, and immunohistochemistry), and mRNA levels (Northern blot analysis and reverse transcription—polymerase chain reaction), was analyzed. When possible, the variance structure, effect size determination, and dose—response modeling of each method of measurement in the laboratory and field were examined. Conclusions from this analysis include: 1) Because of interlaboratory and interspecies variability, general end-point determinations will need to be defined in terms of the statistically detectable fold-change of measurements relative to control or reference values, and 2) fold-change in EROD activity provides the most robust measure of the dose responsiveness of aromatic hydrocarbons within specific chemical classes (e.g., polycyclic aromatic hydrocarbons). The relationship between the ability to measure statistical differences in induction level and the biological significance of those measurements has yet to be defined. To utilize these biomarkers in a risk assessment context, this relationship must be addressed at the scientific and management levels.