We report the isolation and characterization of a new homeobox gene from Arabidopsis thaliana using a polymerase chain reaction (PCR) cloning strategy. The full-length cDNA, designated Athb-12, encodes a protein of 235 amino acids. It contains the conserved DNA binding domain and the leucine zipper motif, characteristic of the homeodomain-leucine zipper family of transcription factors. The deduced amino acid sequence of Athb-12 shows over 80% identity to the Arabidopsis Athb-7 in the homeodomain (82%) and the leucine zipper motif (80%) of the proteins. However, outside the homeodomain and the leucine zipper motif, the homology is significantly lower. RNA analysis identified only one 0.96 kb transcript consistent with the size of Athb-12 cDNA. The Athb-12 transcript was detected in stem, leaf, flower and root as well as in seedlings. Treatment with water stress and exogenous abscisic acid (ABA) resulted in the accumulation of Athb-12 mRNA, similar to that of Athb-7. However, the time course of the Athb-12 response to ABA differed from that of Athb-7, suggesting that both genes, in response to ABA, are regulated in different manners. Taken together, these data suggest that Athb-12 and Athb-7 are members of a related gene family involved in the plant's response to water stress.