Eleven contributions review our knowledge of the characterization of glycoprotein hormone microheterogeneity, the relationships between biological activity and microheterogeneity, the endocrinological control mechanisms involved in the production of these forms and the underlying biochemical basis for glycoprotein hormone microheterogeneity. Organized so that the heterogeneity of each hormone from a variety of species is covered in detail, the peptide components and oligosaccaride stuctures of glycoprotein hormones are reviewed, and the heterogeneity of uncombined alpha and beta subunits is discussed.