This paper discusses a novel application of PIGE for the determination of ¹³C in breath sample. Samples of human breath, urea, glucose, benzamide, barium carbonate were analyzed against tank CO₂ and graphite standard. An accuracy check of the ¹³C determination (with reference to mass spectrometric "True" results) gave a relative error of only- 0.4% for PIGE. The performance of different standard in this determination was assessed. Relative standard deviation for the determination of ¹³C isotopic abundance in breath samples were <20%. Then, if a 25% change is conservatively assumed observable in ¹³C abundance, an increase in ¹³C percent isotopic abundance from the natural 1.11% (average) to only 1.39% may be detected.