Crystals of recombinant human interleukin 10 have been grown from solutions of ammonium sulfate. The crystals are tetragonal, space group P41212 or P43212; the unit cell axes are a = 36.5 Å and c = 221.9 Å. There is the equivalent of one polypeptide chain in the asymmetric unit. The crystals are stable to X‐rays and diffract to at least 2.5 Å resolution. © 1995 Wiley‐Liss, Inc. Copyright © 1995 Wiley‐Liss, Inc.