A comparative genome analysis on exon-intron distribution profiles is performed for human and mouse genomes to deduce similarities and differences between them. Interestingly, both in human and mouse genomes, the total length in introns and intergenic DNA on each chromosome is significantly correlated to the chromosome size. The results presented provide a framework for understanding the nature and patterns of exon-intron length distributions, the constraints on them and their role in genome design and evolution.