Secretion of pre-folded extracellular proteins across the outer membrane of Gram-negative bacteria is mainly assisted by the type II secretion machinery composed of 12-15 proteins. Here, the crystallization and preliminary analysis of one of the essential components of Xanthomonas campestris secretion machinery, the 21 kDa N-terminal domain of XpsE protein (XpsE(N)), are reported. XpsE(N) has been crystallized at 277 K using PEG 400 as precipitant. These crystals belong to the tetragonal space group P4(1)2(1)2 (or P4(3)2(1)2), with unit-cell parameters a = b = 56.1, c = 102.7 A. A 98.5% complete native data set from a frozen crystal has been collected to 2.0 A resolution at 100 K with an overall R(merge) of 5.0%. The presence of one subunit of XpsE(N) per asymmetric unit gives a crystal volume per protein weight (V(M)) of 1.92 A(3) Da(-1) and a solvent content of 36.1%.