Vernalization promotes early flowering in late ecotypes of Arabidopsis thaliana. The mechanisms of vernalization are poorly understood. A subtractive hybridization approach was used to isolate vernalization-responsive genes from a late-flowering ecotype of Arabidopsis thaliana based on the premise that transcript levels of such genes would increase with cold treatment and remain high even after removal of the vernalization stimulus. EARLI1 is the first Arabidopsis gene shown to be stably activated by vernalization. The abundance of its RNA is progressively elevated by vernalization and remains high for at least 20 days at room temperature. The basal level of EARLI1 RNA is higher in early-flowering ecotypes, but is increased also after vernalization. Vernalization and subsequent growth in long-day photoperiods have an additive or synergistic effect on EARLI1 activation. EARLI1 RNA levels are also transiently induced by brief exposures to cold, but not to abscisic acid. EARLI1 is thus a novel vernalization-responsive gene in Arabidopsis thaliana that can be used to investigate vernalization-specific transcriptional regulation.