This study examines the predictive value of conflict and conflict-related variations in negative emotion dynamics, with respect to three cortisol indicators (cortisol awakening responses; overall cortisol output; diurnal cortisol slopes). A total of 166 workers provided momentary reports on conflict(s) with colleagues and negative emotions 10 times a day for 2 workdays and salivary cortisol samples 5 times a day. The results of latent growth curve piecewise multilevel models revealed that the occurrence of a conflict and the number of conflicts introduced significant variations in specific cortisol parameters indicating greater cortisol levels throughout the day. Moreover, the conflict-elicited negative emotion boost predicted a lower reduction of cortisol levels from morning to evening. Last, the postconflict decline in negative emotions was negatively associated with overall cortisol production. This study contributes to establishing a potential association between naturally occurring episodic conflicts at work and daily cortisol patterns, identifying within-person fluctuations in negative emotions as psychological mechanisms through which this occurs. (PsycInfo Database Record (c) 2023 APA, all rights reserved).