Parallel pumping in the region below 500 MHz provides a convenient tool for measuring the elastic and magnetic relaxation parameters of low‐loss ferrities and garnets. This frequency region is of particular interest in microwave acoustic and cylindrical domain applications and is not readily accessible by conventional resonance and pulse‐propagation techniques. We find that the usual treatments of parallel pumping, in which the normal modes are considered to be plane waves, fail at low frequencies because of multiple surface reflections. A theory is developed which does not contain the plane‐wave assumption and is found to agree with our experimental results for YIG. Our experiments were performed at room temperature with a pump frequency of 42 MHz. The magnetic relaxation parameter determined from these experiments is two orders of magnitude larger than the value that would be deduced from microwave uniform‐precession resonance measurements and is in accord with the domain wall mobility measurements of Hagedorn and Gyorgy, Wanas, and Vella‐Coleiroet al.