The galactose-binding lectin EW29 from the earthworm Lumbricus terrestris is composed of two homologous domains, both of which are members of the R-type lectin family. The truncated mutant rC-half comprising the C-terminal domain was crystallized by the hanging-drop vapour-diffusion method. The crystal belonged to space group P4(3)2(1)2, with unit-cell parameters a = b = 61.2, c = 175.6 A, and diffracted to beyond 1.9 A resolution. Matthews coefficient calculations suggested that this crystal contained two molecules per asymmetric unit.