The frequency response curves (FRC) of isolated blood vessels differ from each other not only in their initial slopes, but in their maxima, and their intercept on the frequency axis. Within the physiological range, there is a linear relation between response and frequency. The FRC of most vessels with junctional innervation are similar, varying only somewhat with innervation density. Other factors found to influence the FRC are: variation in innervation distribution, in the extent of myogenic propragation, and large differences in the sensitivity of the alpha-adrenergic receptor. The effectiveness of the transmitter increases with frequency rise. The maximum effective radius of the transmitter released from one varicosity is only several microns. In vessels with light to moderate innervation density at low frequencies, there is probably little overlap of transmitter effect from adjacent varicosities even at the outermost layers of smooth muscle cells. There is a disparity between neurogenic response and that which might be expected from the direct action of the transmitter. It is proposed that a local limited myogenic extension of excitation may extend the local action of a quantum of transmitter.