Background: Parkinson's Disease (PD) is a progressive, neurodegenerative condition most commonly affecting adults over 60 years of age. PD patients often experience an increase in muscular fatigability as well as a decrease in muscular strength and power output. Beta-alanine (BA) has been shown to decrease muscular fatigue by increasing intra-muscular carnosine levels. Carnosine is thought to improve measures of fatigue, strength, and power in populations ranging from elite athletes to the elderly by attenuating the decrease in pH within working skeletal muscle. Purpose: To examine the effect of 4 weeks of beta alanine (BA) supplementation on muscular performance, submaximal oxygen consumption (VO2), and body composition in adults diagnosed with PD. Methods: In this double blind placebo controlled study, participants with PD were stratified by leg strength and randomly assigned to either a SRCarnoSyn ® (Sustained Release) beta-alanine group (BA; age, 68.0 ± 9.2 years; 5 men, 4 women) or a maltodextrin placebo group (PL; age, 68.0 ± 8.9 years; 8 men, 2 women). Both groups took two 800 mg pills, three times/day with meals (4800 mg/day). No other nutritional or exercise changes were introduced. Before and after four weeks of supplementation, the following laboratory tests were conducted: anthropometrics, body composition (DXA), anaerobic capacity (Wingate), submaximal oxygen consumption (YMCA), leg strength, power, and fatigue (Biodex), and a 6-minute walk test. Results: Significant group by time interactions were observed for total body fat percent (BA: 35.2 ± 6.5 vs. 35.5 ± 6.6%; PL: 30.2 ±8.0 vs. 29.3 ±8.1%, p=0.01); android fat percent (BA: 39.5 ±11.4 vs. 40.5 ±11.2%; PL: 34.3 ±11.7 vs. 32.4 ±12.9%, p=0.01); and total fat-free mass (BA: 51.6 ±9.9 vs. 51.0 ±10.2kg; PL: 53.0 ± 8.9 vs. 53.9 ± 9.4kg, p=0.004). In addition, significant group x time interactions were observed during the 180 degrees/sec isokinetic fatigue test for both the percent work relative to bodyweight during flexion (BA: 57.5 ± 15.4 vs. 55.2 ± 13.6%; PL: 52.9 ± 22.3 vs. 62.0 ± 21.7%, p=0.02) and acceleration time during extension (BA:67.8 ±19.9 vs. 72.2 ± 23.9 msec ; PL:85.0 ± 22.2 vs. 72.0 ± 20.4 msec, p<0.05). The following significant time effects were measured: fat mass; six-minute walk test distance; isokinetic 60 degrees/second test: peak torque during flexion; average peak torque during; relative peak torque during flexion; total work during; average power during both extension and flexion; as well as deceleration time during extension;180 degrees/second test: peak torque during extension; average peak torque during extension; relative peak torque during; total work during both and flexion; average power during both extension and flexion; acceleration time during both extension and flexion; as well as deceleration time during extension; isometric 60 degree test: peak torque away and relative average peak torque away; and the fatigue test; peak torque during extension; relative peak torque during extension; relative total work during extension; and acceleration time during extension. No other significant time effects were observed and no differences were observed between groups. Conclusion: Four weeks of BA supplementation did not improve markers of muscular performance, submaximal oxygen consumption, or body composition in patients with PD to a greater degree than PL.