The variation of the pattern of the rhythmic diameter changes, in the hamster skin fold window preparation, was studied sequentially along the branching network of the arterial vessels, from A1 small arteries (70-100 micron diameter) to A4 terminal arterioles (less than 15 micron diameter). Contraction and dilation waveforms were characterized at all subsequent levels of bifurcation. The frequency of vasomotion was determined by a specialized spectral method called PRONY, which approximates the spectral composition of complex waveforms by the least square criteria and estimates the coefficient of correlation between reconstructed and original data. It was found that the frequency of vasomotion changes abruptly at the branching points, systematically increasing in the downstream direction. The power spectrum showed that the frequencies, which appear to originate at the bifurcations and have maximum amplitude at these points, are also found in the upstream waveforms. The downstream propagation of contractions and dilations causes superposition of waves. Thus the pattern of vasomotion is the composite effect of signals that originate at various branching points and spread downstream and upstream in the microvasculature. It seems likely to suggest that single unit smooth muscle cells, located at the branchings (local pacemakers), control the arterial rhythmic diameter changes. This time dependent phenomenon affects deeply the microvascular blood flow.