This paper presents typical data on the internal friction of twelve single crystals of zinc oscillating longitudinally. The measurements of decrement were made at frequencies of 41 kc and 57 kc. (a) Zinc of three grades of purity was used. The behavior of decrement as a function of stress amplitude for these different materials was found to depend less on the purity of the metal than has been reported previously (see references 1 and 2). (b) For one crystal the decrement showed little rise from its initial value of 2×10−5at very low stress amplitudes up to stress amplitudes nearly three times the static elastic limit. Considerable similarity of behavior of the decrement as a function of stress amplitude resolved into the basal plane has been found for a number of crystals with a wide range of orientation. The obtaining of these consistent results depended on the use of appropriate annealing and etching techniques. (c) The decrement of a well annealed crystal increased with rising temperature at all stress amplitudes throughout the temperature range −75°C to 150°C. (d) The prior application of static stress far below the static elastic limit has been found to increase the decrement at high stress amplitudes without affecting that at very low stress amplitudes. This increase was a function of the stress amplitude at which the decrement was measured, and of the prior static stress,L. The observations fitted a relation of the form log&Dgr;=C1+C2L, whereC1depended on the amplitude of measurement andC2was approximately constant.