Histology incorporates microtechnique, the preparation of living material for observation and microscopy to study the anatomy of cells, tissues and organs. Interpreting histological patterns in a specimen may help to correlate form and function at the cellular, tissue and organ levels. Many stain options and staining methods (“schedules”) for plant tissues have been described previously (Johansen, 1940; Jensen, 1962; O’Brien and McCully, 1981; Sylvester and Ruzin, 1994; Ruzin, 1999). Here, we present a straightforward, inexpensive protocol that uses Toluidine Blue O (TBO) to stain maize tissue. TBO is a general metachromatic stain that can be used on paraffin-embedded histological sections, as well as fixed, hand-sectioned material. The value of TBO as a stain is the inherent metachromasia, whereby the dye is altered by pH resulting in violet blue color variants. This property is particularly useful even in sectioned material for identifying acidic components of plant cells. We demonstrate the utility of TBO staining for cellular-, tissue- and organ-level studies using maize seedling root, shoot apex and mature leaf (Figure 2).