Microarray technology enables us to monitor large changes in transcripts at any given time. The compilation of these data makes possible the comparison of such gene expression data on a genome-wide scale. As comparisons of genome sequence data yield new biological insights, comparative analyses of transcriptome data also promise new discoveries regarding metabolic pathways and cellular processes. The coordinated expression of genes shows that these genes physically interact with each other or are part of the same cascade. We have produced one of the largest expression profiles of adult mice and developmental tissues. These data, as well as the data on yeast from previous reports, were used to see whether coordinated expression (with high correlation coefficient) is closely coupled to the actual cascade on the pathway map.