Asbtract:  The problem of finding periodically expressed genes is at the center of numerous efforts to identify the molecular components of biological clocks. We present an approach to this problem appropriate for analyzing microarray data, based on the cyclohedron test, which is a rank test inspired by recent advances in algebraic combinatorics. This talk will highlight the statistics and combinatorics that underlie the cyclohedron test and its implementation, in light of multiple hypothesis testing concerns. No prior knowledge of microarray data analysis, combinatorics, or multiple testing will be assumed.