According to current regulatory concepts, pulsatile ACTH concentrations (con) stimulate time-lagged cortisol secretion rates (sec) via an implicit con-sec dose-response relationship. The present analyses reconstruct nonlinear properties of this in vivo agonist-response interface noninvasively in order to investigate pulse-by-pulse coupling consistency and to obviate the need to infuse isotopes or exogenous effectors, which may disrupt pathway interactions. This approach required an ensemble strategy of: (i) measuring ACTH and cortisol con in plasma sampled every 10 min for 24 hr in 32 healthy adults; and (ii) estimating simultaneously: (a) variable-waveform ACTH and cortisol sec bursts superimposed upon fixed basal sec; (b) biexponential kinetics of ACTH and cortisol disappearance; (c) nonequilibrium exchange of cortisol among free, CBG and albumin-bound moieties; (d) two sec-burst shapes demarcated by a statistically defined day-night boundary; (e) feedforward efficacy, potency and sensitivity; and (f) stochastic variability in feedforward measures overtime. Thereby, we estimate: (i) ACTH sec (µg/L/day) of 0.27 ± 0.04 basal and 0.87 ± 0.07 pulsatile [mean ± SEM]; (ii) cortisol sec (µmol/L/day) of 0.10 ± 0.01 basal and 3.5 ± 0.20 pulsatile; (iii) free cortisol half-lives (min) of 1.8 ± 0.20 (diffusion/advection) and 4.1 ± 0.30 (elimination) and a half-life of total cortisol of 49 ± 2.4 and of ACTH of 20 ± 1.3; (iv) ACTH potency (EC₅₀, ng/L) of 26 ± 2.4, efficacy (nmol/L/min) 10 ± 1.8, and sensitivity (slope units) 0.65 ± 0.09; (v) night/day augmentation of ACTH and cortisol sec-burst mass by 2.1- and 1.7-fold [median]; (vi) abbreviation of the modal time to maximal ACTH and cortisol sec rates by 4.4- and 4.3-fold, respectively, after a changepoint clocktime of 0205 h [median]; (vii) in vivo percentage distribution of cortisol as 6% free, 14% albumin- and 80% CBG-bound with an absolute free cortisol con (nmol/L) 11.5 ± 0.54; and (viii) significant [mean CV] stochastic variability in feedforward efficacy [140%], potency [38%] and sensitivity [56%] within the succession of paired ACTH/cortisol pulses of any given subject. In conclusion, the present composite formulation illustrates a platform for dissecting mechanisms of in vivo regulation of effector-response properties noninvasively in the corticotropic axis of the uninfused individual.