We used a PCR-based subtraction cloning procedure with concanavalin A-treated and -untreated animal caps from stage 9 Xenopus embryos to search for genes up-regulated during early neural development. One such gene was found to encode a protein homologous to several known glutamine synthetases, and we named it xGS. Molecular hybridization studies revealed that xGS mRNA is maternally transmitted and abundantly expressed in neuroectoderm-derived tissues during the gastrula and neurula stages. The expression of xGS mRNA in the nervous system continues until the larval stages, but declines thereafter and becomes undetectable in adult brain. Considering its metabolic activity and potential neuroprotective effect against the neurotoxic substances such as glutamate and ammonia, the glutamine synthetase may play an important role in the early stages of vertebrate neural development.