As a result of the progress in sequencing technology, many plant genomes have now been determined. Functional genomics is required to clarify gene function in many of these species. To identify useful genes easily and quickly, we have developed a FOX (f ull-length cDNA o verex pressor) hunting system in which full-length cDNAs are overexpressed in Arabidopsis plants. This system was applied to high-throughput analysis of rice genes through heterologous expression in Arabidopsis (rice FOX Arabidopsis lines). We demonstrated that it is possible to carry out high-throughput analysis of gene function by utilizing rice FOX Arabidopsis lines. In this protocol, we describe how to isolate candidate rice FOX Arabidopsis lines and to determine the rice fl-cDNA that is responsible for the observed phenotype.