Many plant species including temperate grasses require vernalization in order to flower. Vernalization is the process of promotion of flowering after exposure to prolonged periods of cold. To investigate the vernalization response in monocots, the expression patterns of about 1,500 unique genes of Lolium perenne were analyzed by a cDNA microarray approach, at different time points after transfer of plants to low temperatures. Vernalization of L. perenne takes around 80 d and, therefore, the plants were incubated at low temperatures for at least 12 weeks. A total of 70 cold-responsive genes were identified that are either up- or down-regulated with a minimal 2-fold difference compared with the common reference. The majority of these genes show a very rapid response to the cold treatment, indicating that their expression is affected by the cold stress and, therefore, these genes are not likely to be involved in the flowering process. Based on hierarchical clustering, one gene could be identified that is down-regulated towards the end of the cold period and, in addition, a few genes have been found that are up-regulated in the last weeks of the cold treatment and, hence, are putative candidates for genes involved in the vernalization response. Three of the up-regulated genes are homologous to members of the MADS box, CONSTANS-like and JUMONJI families of transcription factors, respectively. The latter two are novel genes not connected previously to vernalization-induced flowering. Furthermore, members of the JUMONJI family of transcription factors have been shown to be involved in chromatin remodeling, suggesting that this molecular mechanism, as in Arabidopsis, plays a role in the regulation of the vernalization response in monocots.