Radioimmunoassay for melatonin.

Rabbits immunized with human albumin conjugates of N-(p-chlorobenzoyl)-2-methyl-5-methoxyindole-3-acetic acid (indomethacin), 5-methoxytryptamine, and 2-methyl-5-methoxyindole-3-acetic acid produced antibodies that bound [3-H] melatonin. The serologic specificities for the binding of melatonin with antibodies from four antisera to these three immunogens were determined. Melatonin was measurable even at the 0.1 picomole level by a radioimmunoassay. Serotonin, N-acetylserotonin, 5-methoxytryptophol, 5-methoxytryptamine and 6-hydroxymelatonin can be ruled out as immunoreactive material with the use of the multiple antisera of different specificities.