Reindeer beta-lactoglobulin (betaLG) belongs to the lipocalin superfamily. Its DNA and protein sequences have been determined and showed that it had nine residue changes from bovine betaLG. Reindeer betaLG, the structure of which was finally determined at 2.1 A resolution in space group P1, crystallized in a unit cell that is both P2-like and P2(1)-like owing to the presence of an almost perfect (but noncrystallographic) body-centring vector. The non-body-centred data could only be observed using a very bright synchrotron beam and a novel refinement strategy was adopted to enable us to use the weak h + k + l = 2n + 1 reflections.