Follicle stimulating hormone is a dimeric glycoprotein hormone which is used widely in reproductive and developmental medicine both as a diagnostic analyte and as a therapeutic product. It is therefore a good example of a clinically important heterogeneous material for which a number of different assay methodologies have been developed. Immunoassays for follicle stimulating hormone (FSH) are used in the diagnosis of disorders of reproduction and development, whereas in vivo bioassays are used for calibration of therapeutic preparations. Different immunoassay systems, based on different formats, exhibit variability in their estimates of activity of FSH which arises from different specificities of antibodies for different forms of FSH which are encountered. In order to minimise between assay variation and to enable better between laboratory comparisons the World Health Organisation (WHO) has issued a series of ampouled preparations of FSH. The availability of these materials has been reviewed previously but on the completion of a recent collaborative study to evaluate candidate standards for rDNA-derived FSH and highly purified urinary FSH (urofollitropin) it is now appropriate to review the current status of these standards and to discuss the future of standardisation for FSH in particular and where appropriate to make reference to other materials.