The microvibration or minor tremor (MT) on the body surface of man and rabbit was recorded under various physiological conditions. The electrocardiogram (ecg) or heart beat and sometimes electroencephalogram (eeg) were also traced simultaneously with the recording of MT to elucidate the physiological significance of the mechanism of the development of MT. In some cases, correlation and frequency analyses were performed on MT to obtain their average time- and frequency-patterns. In MT tracings under the relaxed condition, 2 groups of vibrations corresponding to the first and second heart beats or the R and T waves of ecg were observed. This synchronization was more evident in the cross-correlogram of the heart beat or ecg and the MT than in the original MT tracing. In the autocorrelograms of MT, a damping of oscillation with a beat phenomenon was clearly shown. In the power spectra of the autocorrelograms, several peaks were recognized in the so-called alpha frequency which confirm the beat oscillation in the autocorrelograms. However, its frequency range was often broader than that of the alpha wave in eeg. Even when the radial pulse was suppressed by pressure on the upper arm, the 2 groups of main vibrations appeared which corresponded to the R and T waves of ecg. This finding suggests that these vibrations are not closely related to the pulse wave and/or other vibrations of the artery caused by the blood flow, but rather related to vibration of the body surface due to the heart beat. During sleep and awake, where inhibition and acceleration of MT were observed, the same correspondence between MT and ecg was demonstrated as in the relaxed state. It was suggested from the above results that the regulating system of the heart beat in addition to so-called muscle tonus might also play an important role in the inhibition and acceleration of MT under various physiological conditions.