Objectives: To analyze the size and density of cervical zygapophyseal joint spaces in asymptomatic subjects using computed tomography (CT) and plain film radiography. The joint spaces were analyzed before manipulation without traction, before manipulation with manual traction, after manipulation without traction, and after manipulation with manual traction. The data obtained before the manipulation were compared with data obtained after the manipulation to determine if significant alterations occurred. Design: Twenty-two asymptomatic subjects were placed into 1 or more of 6 possible experimental groups. In all experimental groups, except for experiment 1, the subjects underwent: (step 1) a premanipulation radiograph and/or CT scan, (step 2) a premanipulation plus traction radiograph and/or CT scan, (step 3) a postmanipulation radiograph and/or CT scan, and (step 4) a postmanipulation plus traction radiograph and/or CT scan. Results: Except for experiment 2, there was no significant change in the width, area, and density values of the zygapophyseal joint spaces immediately after the manipulation in either the traction or traction-free positions of the neck, and no visible radiolucent cavities were demonstrated in any view. Conclusion: No evidence of gas in the joint space or obvious increase in zygapophyseal joint space width immediately after the manipulation was found. This was evident in both the traction and traction-free postmanipulation scans and plain film images. This is not consistent with the current understanding of cavitation in joints, in particular, the refractory period.