Associations of inter- and intra-individual differences in anxiety and fear with within subject variability in breathing parameters were explored. Timing and volume components of respiration and FETCO2 were measured non-intrusively before and during anxious and fearful imagery in 98 young women. Trait anxiety was associated with less variability in several breathing parameters during baseline preceding imagery. Significant decreases in the variability of expiratory time and inspiratory drive were also observed during anxious imagery. During fearful imagery, however, the variability of FETCO2 increased compared to baseline. Results on anxiety are largely in agreement with models that posit that healthy systems are characterized by variability and flexibility. The paradoxical findings for fearful imagery enhance the importance of a distinction between fearful and anxious affects. (c) 2006 Elsevier Inc. All rights reserved.