To determine whether an approach, such as the modified Oxford technique, can consistently produce data that reveals the nonlinear nature of the cardiovagal baroreflex, and to ascertain whether the model parameters provide unique insight to baroreflex function, we retrospectively examined 91 baroreflex trials (38 subjects; age range 22-72 years; 27 men and 11 women). The modified Oxford technique was used (bolus sodium nitroprusside followed by bolus phenylephrine) to perturb blood pressure and the resulting systolic blood pressure - R-R interval responses were plotted and modeled using a linear, a 4-parameter symmetric, and a 5-parameter asymmetric model. Several issues were examined during reflex modeling, such as the effect of data averaging, various approaches to gain estimation, and the predictive value of model parameters. Sigmoid models accounted for a greater amount of the variance than did the linear model: linear r² = 0.81±0.01, 4-parameter r² = 0.90±0.08, 5-parameter r² = 0.90±0.08 (p < 0.05 linear vs. sigmoid models). Data averaging did not affect model fits. While the four gain estimates (linear remodel, 1^st derivative, peak, set point) were statistically related, the set point gain was significantly lower than other estimates (p<0.05). Subgroup comparisons between young and older healthy subjects revealed differences in all indices of cardiovagal baroreflex gain, as well as R-R interval operating range and curvature parameters. In conclusion, the modified Oxford technique consistently reveals the non-linear nature of the human cardiovagal baroreflex. Moreover, of the parameters produced by the symmetric sigmoid model, only the response range provides unique information beyond that of reflex gain.