A 6‐MeV electron beam with current of 100‐200 A was used to study the hose instability of a relativistic electron stream. The growth rates of the instability were experimentally determined, and measured values displayed the trends predicted by theoretical analyses. The magnitude and position of the maximum growth rate as related to the perturbing frequency and plasma‐current decay times agreed well with the predictions of both the rigid and nonrigid beam models. The general dependence of growth rate on the ratio of channel radius to beam radius was observed.