Figure 3a.Average concentrations of melatonin in plasma (black, average N=133), saliva (blue, average N=28) and 6-sulphatoxymelatonin (aMT6s) in urine (red, average N=88), all measurements by radioimmunoassay. Diagrammatic representation of mean normal values (healthy men and women over 18 years old) from the author’s laboratory.