Objective:This study examined the within-person relations between transitory changes in mood, asthma symptoms, and peak expiratory flow rate (PEFR).Methods:Thrice-daily for 21 consecutive days, 48 adults with moderate to severe asthma entered information in palm-top computers about their mood and asthma symptoms. A multidimensional model of mood, ie, the mood circumplex, informed the assessment of mood arousal and mood pleasantness. At each observation, participants also recorded their PEFR with peak flow meters that stored blinded data. Albuterol doses were also monitored electronically. Before and after the 21-day study, spirometric measures of airways obstruction were taken under controlled conditions.Results:Random effects regression models revealed a significant, but weak, within-person relation between symptoms and PEFR. Changes in mood vectors with an arousal component were significantly related to PEFR changes, whereas changes in mood vectors with a pleasantness component tracked changes in asthma symptom reports, even after adjustment for contemporaneous PEFR and after controlling for time of day and albuterol dosing. Comparison of spirometric assessments with unsupervised PEFR suggested that part of the relation between mood arousal and PEFR may be attributable to the “effort-dependence” of peak flow self-monitoring.Conclusions:Different dimensions of mood were associated with transitory changes in asthma symptoms and PEFR. This may be one reason why individuals with asthma misperceive the severity of their symptoms in relation to underlying airways obstruction.