Metamorphosis of sea urchin, Hemicentrotus pulcherrimus, can beinduced by L-glutamine. In metamorphosis, arms retracted initially and anteriorandposterior- cilialy bands retracted finally. I report that retracting orpresumptive retracting tissues of larvae show apoptosis during metamorphosis ofH. pulcherrimus. When larvae were treated with glutamine, the apoptotic features,pycnonosis of chromatin and DNA fragmentation, were observed in arms earliest,and in anterior- and posterior- cilialy bands latest. These results suggest thatapoptosis is important in retraction of larval tissue during metamorphosis of seaurchin.