AbstractMorphometric measurements of cellular area, nuclear area and nuclear:cytoplasmatic ratio were performed on single cells in pleural effusions from 15 patients with effusion caused by bronchial, ovarian, or mammary carcinoma. The results were compared with corresponding measurements on mesothelial cells in pleural effusions from 15 patients without malignant disease. Significant differences were found between the mean values from cellular area, nuclear area, and nuclear:cytoplasmatic ratios in mesothelial cells from benign effusion versus malignant cells from effusions associated with metastatic growth. Such morphometric measurements are, however, of little value in routine diagnostic work as more than 90% of the cells in the two groups showed similar values. Diagn Cytopathol 1987;3:50–5