The confocal laser scanning microscope (CLSM) has become a vital instrument for the examination of subcellular structure, especially in fluorescently stained cells. Because of its ability to markedly reduce out-of-focus flare, when compared to the conventional wide-field fluorescence microscope, the CLSM provides a substantial improvement in resolution along the "z" axis and permits optical sectioning of cells. These developments have been particularly helpful for the investigation of plant cells and tissues, which because of their shape, size, and optical properties have been difficult to analyze at high resolution by conventional means. We review the contribution that the CLSM has made to the study of plant cells. We first consider the principle of operation of the CLSM, including a discussion of image processing, and of lasers and appropriate fluorescent dyes. We then summarize several studies of both fixed and live plant cells in which the instrument has provided new or much clearer information about cellular substructure than has been possible heretofore. Attention is given to the visualization of different components, including especially the cytoskeleton, endomembranes, nuclear components, and relevant ions, and their changes in relationship to physiological and developmental processes. We conclude with an effort to anticipate advances in technology that will improve and extend the performance of the CLSM. In addition to the usual bibliography, we provide internet addresses for information about the CLSM.