The initial effectiveness as well as the temporal stability of the effect of cervical spinal manipulation with respect to the amelioration of goniometrically verified cervical lateral-flexion passive end-range asymmetry was examined. Responses of two groups of pain-free subjects were compared: a) those exhibiting end-range asymmetries of greater than 10 degrees who, in addition, had suffered previous neck trauma, and: b) those who happened to exhibit end-range asymmetries of greater than 10 degrees but who had no history of prior neck trauma. All subjects received a single lower cervical adjustment delivered to the side of most-restricted end-range, and goniometric reassessments were performed 30 minutes, 4 hours and 48 hours, following the adjustment. A dramatic amelioration of asymmetry was observed in both groups at 30 minutes and 4 hours post-manipulation. Furthermore, the magnitudes of these short-term effects were similar for the two groups. However, by 24 hours, a difference in the temporal responses of the groups had become readily apparent. By 48 hours, the difference was even more striking; whereas 14 of 16 of the subjects with no previous neck trauma continued to exhibit asymmetries of less than 10 degrees (mean +/- SEM = 3.8 +/- 1.0 degree), 12 of the 16 subjects with previous neck trauma had regained asymmetries of greater than 10 degrees (mean +/- SEM = 11.4 +/- 1.7 degrees). These results indicate that among asymptomatic (pain-free) individuals, the mere presence of passive end-range asymmetry as well as the magnitude of the short-term ameliorative effect of cervical manipulation do not distinguish these two categories of subjects. On the other hand, over long periods of time following manipulation, there appears to be a tendency of individuals who have suffered previous neck trauma to re-establish their aberrant cervical motion characteristics. The possible clinical relevance of these findings is discussed, and suggestions put forth regarding the definition of chronic cervical motion dysfunction. Possible mechanisms (e.g. spinal learning) which may be responsible for this condition are also addressed.