The expression during development of 3 genes located on mouse chromosome 16 (MMU 16) which are implicated in neurobiological processes was examined by blot hybridization beginning at early gestational ages in the mouse. The 3 genes, amyloid precursor protein (App), preprosomatostatin (Smst), and growth-associated protein 43 (Gap43), exhibited distinct profiles of expression. App expression increased steadily throughout fetal and postnatal development. Smst expression peaked during the third postnatal week, then reached a plateau at a slightly lower level in adults, and Gap43 expression was highest in the early postnatal period, declining in adults to levels below those seen at the earliest timepoints examined. Smst message levels exhibited a 1.5-fold increase in the brains of trisomy 16 (Ts16) mice as compared to normal littermates on day 15 of gestation, while Gap43 and App message levels were elevated approximately 2-fold.