A unique torsional-loading apparatus with a strain resolution of 1 × 10 −9 was used to study the continuous, room temperature, initial yielding behavior of tubular zinc monocrystals having axes along [0001] and 〈101̄0〉 directions. At load rates in the range of 0.02 to 0.03 g/mm 2/sec, specimens oriented for basal slip exhibited plastic bursts of the order of 10 −9 in strain units beginning at stresses as low as 0.02 g/mm 2. The magnitude and frequency of occurrence of the millimicroplastic bursts were, in general, found to increase with increasing stress out to nearly the easy glide region. The largest burst recorded was about 2 × 10 −7 in strain units, which is still too small to have been observed by ordinary techniques. Millimicroplastic burst activity was also observed in such specimens under room temperature creep conditions and, to a much less extent, in specimens oriented for non-basal slip. In the latter case {112̄2} 〈1125〉 slip systems are thought to be the most important for specimens deformed in torsion about 〈101̄0〉 axes. In all cases, the burst activity was found to be irreversible and to disappear with iterative stressing in a given stress range, demonstrating the work hardening process. Various yielding models are considered. Depinning of dislocations from impurity atmospheres followed by thermally activated glide through randomly distributed trace impurities seem to offer the best explanation of the initial plastic behavior observed in crystals twisted about the [0001]. The millimicroplastic bursts are thought to result from extensive dislocation movement triggered sporadically in an unstable network by certain local glide events in the basal plane.