Salivary cortisol level was analysed by means of a cortisol salivary immunoassay kit (for more details, see method). (A) Salivary cortisol samples were collected at three particular time points (8 am, 2 pm and 10 pm). Most subjects showed lower cortisol levels at 10 pm compared to that of 2 pm (low cortisol10 pm, n = 33 subjects). Eleven subjects showed higher cortisol levels at 10 pm compared to that of 2 pm (high cortisol10 pm). (B) Cortisol10 pm indicates normalized 10 pm cortisol level (percent of 2 pm cortisol level). Error bars indicate s.e.m. Significant difference at *P < 0.01, **P < 0.0001.