Certain proprioceptive sense is utilized in localizing a part of the limb passively held in space. In the previous study (Hirayama, Fukutake, et al., 1986), we demonstrated that such kind of proprioception, which we called "proprioceptive localization", could be detected by making the patient pick up the thumb with the opposite fingers (the thumb localizing test, TLT). As a further development of the TLT, another test, named a big-toe localizing test (BTLT), was devised. In the BTLT, the patient, with eyes closed and a lower limb passively immobilized by the examiner (the fixed limb), is asked to point to the big toe with the index finger of one hand or the other (the reaching limb). Firstly, we assessed the unselected series of 33 patients with thoracic or lumbar myelopathy regarding their sensory impairment and obtained the following conclusions on the BTLT similar to those in our previous study on the TLT. (1) BTLT deficits results from perceptive impairment in the fixed limb. (2) The perceptual information involved in the proprioceptive localization is different from that of the test for the appreciation of passive movement and posture. (3) On the basis of the correlation to other symptomatology, it is suggested that BTLT deficits arise from lesions of the posterior column-medical lemniscal system. (4) The BTLT is more sensitive than the test for the appreciation of passive movement and posture. Secondly, we evaluated another unselected series of 63 patients with unilateral TLT deficits due to CNS lesions. Eight patterns of BTLT deficits were identified and classified into 3 following types.(ABSTRACT TRUNCATED AT 250 WORDS)