An important question in the effective use of quantitation in cytology is how to make the link between mathematical parameters and the cytologist. As an example, an investigation is discussed in which cell images from benign mesothelial proliferations were distinguished by quantitative characteristics from those of malignant mesotheliomas originating in the pleura and peritoneum. The significant differences between the three groups in nuclear size, cytoplasmic size and nuclear-cytoplasmic (N/C) ratio could partly be explained by the vacuolation patterns of the exfoliated mesothelial cells in each. Moreover, the primary site of the tumor could be predicted by the quantitative cell parameters. The characteristics of cytologic images, once known to be important, are easily incorporated into standard diagnosis. Thus it now seems possible for the cytologist to differentiate between the three groups by using the cytomorphologic features that relate to the computed parameters. This shows the value of translating computerized parameters into cytomorphologic criteria.