In six male physically active subjects the adrenocortical and metabolic changes in response to incremental exercise testing were investigated. Blood and saliva samples were taken at rest, at the end of every workload (duration 4 min with 50 W increment), immediately and 10 min after 1 min all out spurt on the electrically braked cycle ergometer. Both saliva and serum cortisol were measured as well as blood lactate. The cortisol response in serum and in saliva showed similar dynamics (r = 0.86, p less than 0.001, n = 50) at submaximal work. At maximal work the serum cortisol concentration showed a transitory decrease, which was not manifested in saliva. It is hypothesized that a factor related to the metabolic acidosis masks the actual adrenocortical response in the serum but not in saliva. Correlation analysis revealed a positive relation between lactate and cortisol in serum (r = 0.56, p less than 0.01, n = 50) and saliva (r = 0.70, p less than 0.01, n = 50). Apparently, salivary cortisol closely reflects plasma free cortisol level, presenting advantage over total cortisol measurements. Moreover salivary measurement will permit studies in their authentic settings and should assist attempts to understand the nature of the adrenocortical function in exercise.