Combination of high pressure liquid chromatography and radioimmunoassay is a powerful tool for the specific and quantitative determination of endorphins and related peptides.

A method for the separation and subsequent quantification of endorphins and related peptides was developed. Separation of the peptides was achieved by high pressure liquid chromatography on a reversed phase column. By virtue of the high resolving capacity of this system peptides differing in only one amino acid residue could be separated easily. For quantification of the isolated peptides specific radioimmunoassay systems were used. The combination of the two techniques was applied to determine specifically a number of endorphin-like peptides in rat pituitary gland. For the first time the presence of des-tyrosine-endorphins in addition to known endorphin fragments is demonstrated.