Among the pituitary hormones, a FSH radioimmunoassay procedure has been established. The labelling and the separation methods are suitable for a FSH radioimmunoassay. However, the gel filtration technique is superior to the starch gel electrophoresis in view of the simplicity, short separation time and the bindability of the purified labelled antigen to its antibody. For the separation of the free antigen from the antibody bound, the double antibody technique could be successfuly applied.