This article describes the methods and techniques used to produce mutagenized mice to conduct high-throughput forward genetic screens for circadian rhythm mutants in the mouse. In particular, we outline methods to safely prepare and administer the chemical mutagen N-nitroso-N-ethylurea (ENU) to mice. We also discuss the importance of selecting mouse strain and outline breeding strategies, logistics, and throughput to produce these mutant mice. Finally, we discuss the breeding strategies that we use to confirm mutation heritability.