Alfalfa is a forage legume for which vegetative biomass is harvested. Stems of Alfalfa have been proposed as a biofuel feedstock for the production of cellulosic ethanol. As stems mature they accumulate higher concentrations of cell wall materials but the digestibility of these cell walls decline. We have established an experimental setting to allow the identification of transcripts of genes implicated in cell wall modification in Alfalfa stems. Two cultivars with particular characteristics related to biomass and climate adaptation were chosen for the analysis. The stems were harvested at four developmental stages (i.e. late vegetative, early bud, late flower and early seed pod) and divided into internodes. At each stage, four internodes were considered for the analysis.  We have used the Agilent Medicago gene expression microarray which contains 43803 long-oligos (60 mers) probes to profile expression patterns in various internodes of the two Alfalfa cultivars. Preliminary results show different patterns of expression along developmental stages and between internodes at each stage analysed. Using bioinformatics tools we will concentrate the analysis on genes that follow a pattern of expression that could be related to cell wall modification. Genes identified as so will eventually be targeted to functional studies toward improving the digestibility of Alfalfa cell wall for cellulosic ethanol.