Functional gastrointestinal disorders (FGIDs) affect millions of people of all ages, regardless of race or gender, but little information related to FGIDs is available and no diagnostic methods exist. Therefore, the aim of this study was to investigate the alterations to gastrointestinal tracts induced by FGIDs, and to identify the feasibility of developing an ultrasonic diagnostic system to detect these alterations. Palpation/percussion examinations and in vitro micro-indentation tests were performed on 40 participants with or without FGIDs and 20 Sprague-Dawley rats with or without simulated FGIDs to identify any alterations to the mechanical response of the gastrointestinal tract. A finite difference analysis was performed for three simple models with or without assumed FGIDs to identify the feasibility of developing an ultrasonic diagnostic system. The results obtained from the palpation/percussion examinations and in vitro micro-indentation tests showed that a gastrointestinal tract with an FGID became more rigid than a healthy tract (p<0.05). The results obtained from the finite difference analysis showed that an ultrasonic diagnostic system for FGIDs effectively detects alterations to the rigidity of the gastrointestinal tract, indicating that the development of an ultrasonic diagnostic system is reasonable and will aid in the diagnosis and treatment of FGIDs.