 Zebrafish have a total of 94 cytochrome P450, CYP, genes, distributed among 18 gene families found also in mammals. These CYPs are involved in endogenous functions such as steroidogenesis, retinoic acid metabolism, and xenobiotic metabolism. Additionally, there are orthologous relationships between zebrafish and humans for certain CYP1s and CYP3s. Furthermore, transcript profiling has shown that the majority of zebrafish CYP genes are expressed in embryos, with waves of expression of different sets of genes over the course of development. This provides a foundation for the use of zebrafish as a model in toxicological, pharmacological, and chemical disease research. This article was authored by Perente Thiago, Zanette Juliano, Kubota Akira, and others.