A phage library of cDNA from Arabidopsis thaliana has been screened with oligodeoxyribonucleotides designed from regions of high homology found in tobacco osmotin and other osmotin-like proteins. One of the selected clones, Atosm34, presents a 734 bp open reading frame encoding a polypeptide of 244 amino acids, including the putative N-terminal signal and C-terminal propeptide sequences. Comparative alignment reveals extensive homologies to osmotin and the osmotin-like proteins found in Solanaceae, and also to a related polypeptide found in soybean. Genomic hybridization suggests that the cDNA obtained here corresponds to a single copy gene, and RNA blot analysis showed that the level of expression is highest in old leaves.