Ace is a collagen-binding bacterial cell surface adhesin from Enterococcus faecalis. The collagen-binding domain of Ace (termed Ace40) and its truncated form Ace19 have been crystallized by the vapor-diffusion hanging-drop method. Ace19 was crystallized in two different crystal forms. A complete 1.65 Å data set has been collected on the orthorhombic crystal form with unit cell parameters a=38.43 b=48.91 and c=83.73 Å. Ace40 was crystallized in the trigonal space group P3121 or P3221 with unit cell parameters a=b=80.24, c=105.91 Å; α=β=90 and γ=120°. A full set of X-ray diffraction data was collected to 2.5 Å. Three heavy atom derivative data sets have been successfully obtained for Ace19 crystals and structural analysis is in progress. © 2002 Elsevier Science B.V. All rights reserved.