J. Oort and J. P. A. Baak This manual is written by pathologists and is meant for pathologists. It deals with a subject that became especially popular in pathology at the end of the last decade: morphometry. Morphometry is defined as the quantitative description of a structure (Weibel, 1969). This structure may be both of macroscopic and micro- scopic size. Strictly, the size of an organ is a morphometric feature. This type of morphometry has long been in use in pathology. Examples ofthis type in diagnostic pathology have been given by Roesle and Roulet (1932). In this manual, however, the term morphometry is used in its re- stricted microscopic meaning, i.e., the quantitative description of micro- scopic images and features. The quantitative analysis of microscopic pic- tures has for a long time been subordinated to the qualitative description. This may partly have been caused by the preference of the human mirld for pattern recognition rather than quantitative appraisal, which leads to judgements based on impressions subconsciously tested against the ob- server's (mental) image of the normal pattern. Another cause may have been the time-consuming difficulties of collecting and computing quanti- tative information. During the past decades the usefulness of quantitative methods in histo- and cytopathology has been stressed for many different subjects. In addition, minicomputers have become widely available and are becoming increasingly inexpensive; the more so since the introduction of micro com- puters.