Background: Using a newly developed high-resolution three-dimensional magnetic detector-system (MAGMA), we observed periodical movements of a small magnetic marker in the human stomach at the typical gastric slow wave frequency, that is 3/min. Thus, we hypothesized that each gastric slow wave induces a motor response which is not strong enough to be detected by conventional methods. Methods: Electrogastrographies (EGG, Medtronic, Minneapolis, USA) for measurement of gastric slow waves and MAGMA (Innovent, Jena, Germany) measurements were simultaneously performed in 21 healthy volunteers (10 males, 40.4 +/- 13.6 yrs, 11 females, 35.8 +/- 11.6 yrs). The MAGMA system contains 27 highly sensitive magnetic field sensors which are able to locate a magnetic pill inside a human body with an accuracy of 5 mm or less in position and 2° in orientation at a frequency of 50 Hz. Results: Gastric transit time of the magnetic marker ranged from 19 to 154 min. The mean dominant EGG frequency while the marker was in the stomach was 2.87+/- 0.15 counts per minute. The mean dominant MAGMA frequency during this interval was nearly identical, that is 2.85+/-0.15 movements per minute. We observed a strong linear correlation between individual dominant EGG and MAGMA frequency (R=0.66, p=0.0011). Conclusions: Our findings suggest that each gastric slow wave induces a minute contraction which is too small to be detected by conventional motility investigations but can be recorded by the MAGMA system. The current slow wave theory which assumes that the slow wave is a pure electrical signal should be reconsidered.