Nineteen low back pain patients and eight patients not suffering from low back pain were given several tests of flexibility and asymmetry by two different examiners. Three criteria of reliability and validity were used: (1) significant agreement between independent observers, (2) significantly different scores in the groups with and without low back pain, and (3) significant improvement following a successful spinal manipulation. Tests of anterior flexion and asymmetry of foot eversion met only the first and second criteria while tests of hamstring tightness and asymmetry of voluntary straight leg raising met only the first and third criteria. Passive and voluntary straight leg raising tests were the only measures that met all three criteria. Therefore, of the objective tests investigated here, only passive or voluntary straight leg raising can be strongly recommended for use in the evaluation of spinal manipulative therapy for low back pain.