We have mapped the spatio-temporal expression of the multidomain serine protease neurotrypsin in the developing mouse by in situ hybridization. On embryonic day (E) 8, mRNA is detected in giant trophoblast cells, later in embryonic mesenchymal tissues. On E11, expression begins in Schwann cell precursors, olfactory epithelium, trigeminal ganglion, and midbrain. The floor plate shows strong expression on E12. Further prenatal development is characterized by rising neurotrypsin mRNA in sensory ganglia and motor neurons. Staining in cerebral cortex emerges around birth and culminates toward the end of the first week with a complex laminar and areal pattern. Expression in peripheral nerves and nonneural tissues vanishes soon after birth and the adult neuronal distribution is gradually established until weaning age. This developmental expression pattern suggests roles of neurotrypsin in morphogenesis of nonneural tissues, as well as in neural development, in particular in axonal target invasion, synaptogenesis, and Schwann cell differentiation.