Full-length human tau-protein kinase I (TPK-I; also known as glycogen synthase kinase-3β, GSK-3β) was produced in E. coli and crystallized. The crystals diffract up to 2.3 Å resolution and belong to the orthorhombic space group , with unit-cell parameters a = 82.9, b = 86.1, c = 178.1 Å measured at 100 K.