Previous research reports an increase in aerobic performance and ventilatory threshold (VT) following β-alanine supplementation. However, these studies have not included highly trained subject pools. PURPOSE: To determine the effect of 30 days of β-alanine supplementation (CarnageTM) on VT and peak aerobic power (VO2 peak) in highly fit aerobic athletes. METHODS: Fourteen male runners and triathletes (28.8 ± 9.8 yrs) were assigned into a β-alanine or Placebo (PL) group. Groups were matched for numbers of runners and triathletes, as well as for VT as a percentage of VO2 peak. β-alanine supplementation consisted of 3000 mg/day for 7 days, and 6000 mg/day for the remaining 23 days. Before and after the supplementation period, subjects performed a continuous, graded cycle ergometry test to determine VO2 peak and VT. VT was determined by the intersection of regression lines drawn to fit the upper and lower portions of the Ventilation vs. VO2 curve. Data was analyzed using a 2 x 2 ANOVA with repeated measures. RESULTS: 30 days of β-alanine supplementation did not increase VO2 peak (4.05 ± 0.6 vs. 4.14 ± 0.6 L/min) as compared to the PL group (3.88 ± 0.2 vs. 3.97 ± 0.2 L/min) (p > 0.05). VT did not significantly improve in either the β-alanine (3.47 ± 0.6 vs. 3.49 ± 0.6 L/min) or PL (3.36 ± 0.2 vs. 3.46 ± 0.1 L/min) group (p > 0.05). CONCLUSIONS: 30 days of β-alanine supplementation had no effect on VO2 peak or VT in highly trained aerobic athletes. The potential efficacy of β-alanine supplementation need to be further investigated in both trained and untrained populations.