Recent research has shown conflicting results regarding the effectiveness of BRNS (CNS, Inc.) on athletic performance. However, those studies have not been conducted using elite endurance athletes. Furthermore, the effects of changes in nasal cross-sectional area (NA) on aerobic performance have not been measured. Therefore, the purpose of this study was to assess the effects of BRNS on performance measures in aerobically trained males to determine whether increases in NA are related to performance improvements. Twenty-nine competitive male distance runners (age = 25.76 ± 5.45 yrs., ht. = 69.43 ± 2.52 in., wt. = 151.14 ± 16.52 lbs.) performed three graded exercise tests on a treadmill under three randomly ordered conditions (BRNS, placebo, control). Subjects and researchers were blinded to the BRNS and placebo conditions. NA was determined by acoustic rhinometry before all three conditions and after application of both strips. Repeated measures ANOVA revealed significant increases in VO2 at ventilatory threshold (VT) (p=.0001; BRNS = 3.44± .37 L/min; placebo = 3.24±.35 L/ min; control = 3.33 ± .43 L/min), percent of VO2max at VT (p=.002; BRNS = 80.98 ± 5.99; placebo = 77.57 ± 6.83; control = 78.30 ± 6.80), and HR at VT (p=.04; BRNS = 165.61 ± 8.91 bpm; placebo = 162.79 ± 9.60 bpm; control = 163.76 ± 8.42 bpm) while wearing the BRNS. No significant differences in peak HR (p=.761), VE (p=.123), or VO2max (p=.334) were observed. When data from subjects under BRNS condition were analyzed, those who demonstrated a change in cross-sectional area>. 15 cm2 ("responders") were separated from those who did not ("non-responders"). Responders (n= 17) showed significant increases in VO2 at VT (p=.0001; BRNS = 3.44 ± .46 L/min; placebo = 3.18 ± .43; control = 3.25 ± .50) and percent of VO2max at VT (p=.04; BRNS = 80.16 ± 6.03; placebo = 76.87 ± 7.40; control = 77.24 ± 6.37). Responders also showed non-significant increases in VO2max (p=.08), VE (p=. 11), and HR at VT (p=. 15) while wearing the active strip, in comparison to placebo and control conditions. Non-responders showed no significant differences in any variables across the three conditions. Our findings demonstrated that BRNS may enhance variables related to aerobic performance. Since responders showed significant improvements in VT variables using the BRNS, significant differences may be attributed to increases in NA. This research provides impetus for further study of individuals responsive to BRNS.