A preliminary field study was conducted to estimate relationships between changes in feelings states occurring from before to after 20- to 30-min bouts of moderate cardiovascular exercise, and two measures of adherence to exercise in 66 adults (Mage=38 yrs, 30% males) initiating regimens of 3x/week. Positive pre- to post-exercise changes in participants' feeling state scores ranged from 0 to 100% (M=73.2%, SD=28.8). Significant positive correlations were found between percentage of positive changes and exercise session attendance (r=0.36, p=0.003), and number of days of adherence to exercise (r=0.37, p=0.002), over 14 weeks. Results were interpreted as supporting principles of operant conditioning, and the possibility of exercise-induced feeling changes having direct reinforcing and punishing properties on the behavior of exercise in adults initiating programs. Accounting for identified correlates of exercise maintenance was suggested for extensions of this research. Applied uses of the abbreviated feeling state measure adapted for this research were suggested, after sufficient replication. © 2005 European College of Sport Science.