Detailed studies on the gene expression control, the exact genomic locations of genes and the modes of the gene rearrangement require isolation of the larger regions of DNA surrounding the genes. For this purpose a cosmid library was constructed using the total genomic DNA from rice and spinach, respectively. Each clone in the libraries contains a 35-45 kb DNA fragment as an insert. In this communication, I discuss the use of the cosmid library to analyze the interorganellar DNA migration and rearrangement. I also discuss the use of the comid library to select the sublibraries, each representing the whole mitochondrial, chloroplast and nuclear genomes for the detailed studies on these three distinct genomes.