The purpose of this paper is to review various morphologic methods that have been used to quantitate pulmonary emphysema. With so many investigators working in the field of clinicopathologic correlations, only confusion can result if these workers describe shnilar experiences by different measurements. For example, it seems quite clear that cor pulmonale may occur in patients with chronic bronchitis who have a" little" emphysema, and it may not occur in patients with chronic bronchitis who have" severe" emphysema (1-3). The interpretation of the amount of emphysema by different examiners in these situations is clearly critical. Similarly, interpretation of epidemiologic data is impossible unless the measurements used by different observers are identical. This situation can only add to confusion. Hopefully, this review may be of value to those who have to read papers about the pathology of chronic lung disease, but who are not immediately involved in morphologic investigation and measurements. This review is based on experience with some of the best known methods.