675 Psychoneuroendocrinological research has provided substantial evidence regarding the role of affective factors in hypothalamic - pituitary - adrenal(HPA) axis activation. These findings are further substantiated by recent neuroanatomical and neuropharmacological research, which strongly implicates the amygdala (a limbic structure known to play a key role in the generation of affective responses) in modulating the activation of the HPA axis during stress. However, investigations of the affect - HPA axis relationship in the context of acute exercise have been scarce. In the present study, 8 well-trained male cyclists (24.0 ± 0.1 yr; VO2peak = 61.4± 0.8 ml·kg-1·min-1) underwent dehydration(≈4% reduction of body weight) and the following day exercised on a cycle ergometer at ≈74% VO2peak to exhaustion, in an ambient temperature of 37 °C (mean duration = 19 mins). Blood samples were drawn before the exercise bout and immediately upon exhaustion, concurrently with the administration of the Circumplex Affect Inventory (CAI; Ekkekakis, 1996). Changes in plasma cortisol (CORT; r = -0.816, P<0.01, 1-tailed), plasma adrenocorticotropin (ACTH; r = -0.707, P<0.05, 1-tailed), and the testosterone: CORT ratio ( r= 0.793, P<0.01, 1-tailed) were associated with shifts along the deactivated pleasant - activated unpleasant affect (DPAU) dimension of the CAI(larger concentration increases and ratio decreases were associated with more activated unpleasant affect, and vice versa). The correlation between DPAU and CORT remained after variance due to changes in rectal temperature( r2 = 0.42, part r = -0.65), plasma lactate( r2 = 0.56, part r = -0.75), heart rate( r2 = 0.58, part r = -0.76), and plasma volume( r2 = 0.58, part r = -0.76) was partialled out of CORT, but not after the variance of an aggregate of these variables was partialled out ( r2 = 0.15, part r = -0.38). These findings indicate a substantial degree of covariation between self-reported affective responses and plasma indices of HPA axis activity in the context of exhaustive exercise and are suggestive of a possible functional relationship.