We have demonstrated that expression of genes involved in starch and storage protein synthesis of the maize (Zea mays L.) endosperm are coordinated. Genetic lesions altering synthetic events in one biosynthetic pathway affect expression of genes in both pathways. Initial studies focused on shrunken2 (sh2) and brittle2 (bt2) mutants because these genes encode subunits of the same enzyme, ADP-glucose pyrophosphorylase. Analysis of various sh2- and bt2- mutant alleles showed that the most severe mutations also conditioned the largest increase in transcripts. The analysis was extended by monitoring the transcripts of the genes, shrunken1 (sh1, structural gene for Suc synthase), sh2, bt2, waxy1 (wx1, structural gene for starch synthase), and those of the large and small zeins in isogenic maize lines at 14, 22, and 30 d postpollination. Endosperms were wild type for all of these genes or contained sh1-, sh2-, bt1-, bt2-, opaque2 (o2-), or amylose-extender1 (ae1-) dull1 (du1-) wx1- mutations. Transcripts increased continually throughout kernel development in the mutants relative to the standard W64A used. Variation in the amount of Suc entering the developing seed also altered transcript amounts. The results indicate that starch and protein biosynthetic genes act in a concerted manner, and both are sensitive to mutationally induced differences.