CD34+ preparations from five different umbilical cord samples were compared with respect to their proteome profile using 2-D gel electrophoresis. Fifty-two protein spots were found to match in all preparations referring to the high heterogeneity of such samples indicating a not fully developed (or instable) proteome of stem cells. All matching spots were Subjected to in-gel digestion and nano-LC-MS/MS sequence analysis, from which 22 proteins were unambiguously identified. (C) 2005 Elsevier Inc. All rights reserved.