Significance Endogenous circadian rhythms have been demonstrated in several model systems, including mammals, insects, and fungi, among many others. Cycles in behavior, physiology and gene expression have also been reported in the nematode Caenorhabditis elegans , although limited by experimental conditions. Here we report the application of a luciferase-based reporter to investigate circadian regulation in C . elegans . Our study demonstrates entrainable, endogenous, and temperature-dependent circadian rhythms in gene expression as well as part of the pathway for synchronization. Our results represent an innovative approach for the study of long-term gene expression in real time in this system, opening the way for novel research in neuroscience and molecular pathways in general, including the precise determination of its elusive circadian clock.