In an effort to further understand the antecedents of psychological stress, this study tested two competing stress formulations. One formulation, called the traditional model, proposes that stress is a multiplicative function of perceived consequences and the degree of disparity between perceived demand and perceived ability. Given high consequences, stress is presumed to reach its maximum when demand is substantially greater than ability (overload) or when ability is substantially greater than demand (underload). The other formulation, the revised model, proposes that stress is a multiplicative function of perceived consequences and the degree of correspondence between perceived demand and perceived ability. Stress is presumed to reach its maximum when high consequences are combined with a close match between demand and ability resulting in high uncertainty. The formulations were tested in a naturally occurring stress setting, a classroom which required students to give class presentations. The results offered substantial support for the proposition that overload situations are stress inducing, no support for the traditional model's position that overload and underload conditions are equally stressing, and no support for the revised model. Also, stress varied independently of perceived consequences. Several methodological issues were discussed, including a crucial one questioning the use of absolute levels of discrepancy rather than signed levels of discrepancy between perceived ability and demand in the models.