The chemotactic cytokine RANTES (Regulated on Activation, Normal T-cell Expressed and Secreted) is a potent chemoattractant and activator of a number of leukocytes, with a molecular mass of 8 kDa. Crystals of this protein have been grown from 100 mM sodium acetate buffer (pH 4·6) containing 200 mM magnesium acetate, with 20% (w/v) PEG 4000 and 6% (v/v) glycerol. The crystals grow as thick rods, which diffract to at least 1·8 Å resolution on a rotating anode X-ray source. The crystals belong to space group P 212121 with unit cell dimensions a = 95·14 Å, b = 57·58 Å and c = 24·01 Å with α = β = γ = 90°. The asymmetric unit contains two molecules of the RANTES monomer, with a VM of 2·0 Å3/Da.