The analysis of stress-responsiveness in plants is an important route to the discovery of genes conferring stress tolerance and their use in breeding programs. Proteomic analysis provides a broad view of plant responses to stress at the level of proteins. In recent years this approach has increased in sensitivity and power as a result of improvements in two-dimensional polyacrylamide gel electrophoresis (2DE), protein detection and quantification, fingerprinting and partial sequencing of proteins by mass spectrometry (MS), bioinformatics, and methods for gene isolation. 2DE provides information on changes in abundance and electrophoretic mobility of proteins, the latter reflecting post-translational modifications such as phosphorylation and free-radical cleavage. Here we review the technical aspects of proteomics and demonstrate its use in analyzing the response of rice plants to drought and salinity. More than 2000 proteins were detected reproducibly in drought-stressed and well-watered leaves. Out of >1000 proteins that were reliably quantified, 42 proteins changed significantly in abundance and/or position. We identified several leaf proteins whose abundance increased significantly during drought and declined on re-watering. The three most marked changes were seen with actin depolymerizing factor, a homologue of the S-like ribonucleases and the chloroplastic glutathione-dependent dehydroascorbate reductase. Proteomic comparisons of salt stress-tolerant and stress-sensitive genotypes revealed numerous constitutive and stress-induced differences in root proteins. Among them was caffeoyl-CoA O-methyltransferase, an enzyme of lignin biosynthesis. The abundance of ascorbate peroxidase was much higher in salt-tolerant Pokkali than in salt-sensitive IR29 in the absence of stress. (C) 2002 Elsevier Science B.V. All rights reserved.