Ultrasonic absorption and velocity measurements have been made in high‐purity liquid sodium, potassium, rubidium, and cesium at temperatures from their melting points to 250°C. Corresponding classical absorption values have also been computed over these ranges of temperature. It has been found that the measured absorption values exceed the classical values by 3%–30%. These excess absorptions are attributed to structural relaxation. The ratio of bulk viscosity to shear viscosity was found to be approximately 2.3 in sodium and potassium, 3.4 in rubidium, and 4 in cesium. Sound velocities are presented as linear functions of temperature. Both observed and classical absorptions are given as quadratic functions of temperature.