Summary This paper provides practical examples of basic stereological methods applied to the human planceta. Systematic random sampling gives all parts the same probability of being represented in the sections obtained for microscopical examination. Isotropy and vertical design are described and formulas provided for calculating volume, surface area, length and number. The importance of counts of particles/cells as a fraction of the reference volume is emphasized, but for unambiguous conclusions, results must be expressed as total quantities. If sampling is correct and optimal, the efficiency of the stereological methods provides unbiased and precise estimates, made from counting no more than about 200 counts in one organ.