The use of lectins (1) in electron microscoplcal histochemistry enables specific questions to be answered about the distribution of carbohydrates in cellular and extracellular components. For example, the occurrence of defined carbohydrate residues in particular stacks of the Golgi apparatus (2), or in particular domains of the rough endoplasmic reticulum (3) as demonstrated by lectins indicate the presence of carbohydrate processing enzymes, and the lectin binding can therefore serve as an indicator of cellular function. Because of these functional Implications, lectins are used as maikers of different cellular populations in studies of development and regenerative processes (4-10), in the analysis of the molecular mechanisms of metastasis (11), and in pathological processes such as the carbohydrate disorder globoid cell leukodystrophy (a lysosomal storage disease) (12).