The purpose of this study was to evaluate the reliability of clinical blood pressure readings and to begin a series of experiments to determine if chiropractic adjustments cause any significant changes in blood pressure. Seventy-five students undergoing routine chiropractic health care at Palmer College of Chiropractic Clinic volunteered to participate in the blood pressure measurement protocol in one 10-minute visit. These subjects were placed into one of two groups, based on the clinical findings from the chiropractic examination. One group, the Experimental group, was formed on the basis that they had subluxations in the cervical spine and also were adjusted specifically for them. The Control group was similar but lacked manipulable cervical subluxations on that particular day and were not adjusted. Clinical and experimental procedures were carried out identically on each group. Subjects were examined by standard Gonstead palpatory methods after 5 minutes of quiet sitting in a cervical chair. Blood pressure was recorded by right arm cuff sphygmomanometer by an experienced chiropractor immediately before and again immediately after either the specific cervical adjustment or the control procedure, which was simply motion palpation. The doctors measuring blood pressures did not know to which group the subject had been assigned. Both systolic and diastolic blood pressures were statistically significantly lowered in the Experimental but not the Control group (p < 0.01). The difference in the mean blood pressures was small and was brought about by 14 of the Experimental subjects who experienced a clinically relevant 10-20 mm hg drop. Reliability of blood pressure measurements by two doctors was established under similar conditions in an additional 25 subjects. Interclass Correlation Coefficients for both intra- and interexaminer reliability were highly significant, indicating that our blood pressure measures were reproducible.