To overcome some of the difficulties encountered in studying single layers of mesothelial cells, a battery of techniques was investigated, assessed, and modified. It was found that two main methods were of value: cell monolayers and surface sections. Imprint monolayers on slides coated with 3% gelatin were considered to provide the optimal imprint for cell kinetics and cytochemical assays at room temperature. On the other hand, slides coated with agar were more satisfactory for cytochemical techniques performed at 37 degrees C. The cell-deposit techniques were excellent for studying mesothelial cells in suspension. Investigation of cultured cells was best achieved by the use of a cell-mat on coverglasses for cytochemistry, while the base of the culture vessel with its own cell-mat monolayer was best for kinetic studies. This investigation demonstrated that maximum information is only gained by employing several different techniques. It also indicates which of these will be of greatest value in assessing any one particular aspect of mesothelial pathobiology.