Interpopulational differences in the concentrations and ratios of salivary and serum progesterone.

Lower concentrations of salivary P in Bolivian women cannot be attributed to lower serum P or cholesterol or to higher cortisol-binding globulin or cortisol (stress) levels than those of the American women. Whether serum or salivary concentrations in the two population groups better reflect availability of P to the tissues is an unresolved question.