Clinical and instrumental evaluation of sensory function before and after percutaneous anterolateral cordotomy at cervical level in man. Sensory perception thresholds were assessed by clinical testing and by quantitative instrumental testing before and after operation in 16 subjects for whom unilateral percutaneous cervical cordotomy was performed for the relief of pain due to malignant disease, and compared with clinical assessments of sensory function. We were able to confirm the association between deficit in pin-prick sensation and pain relief in the majority of instances, though the completeness or otherwise of pain relief does not correspond to absence of pin-prick sensation. There is no objective interference with low threshold mechanical sensation as measured instrumentally, although cordotomised subjects do not experience startle, tickle, or cutaneous erotic sensation when subjected to appropriate low intensity tactile sensation. Quantitative instrumental testing shows that the greatest deficits produced by cordotomy are in the sensations of skinfold pinch (? = tissue-damage pain) and skin cooling. The latter is transduced in the periphery by A delta fibres; sensations of warmth and hot pain, transduced by primary afferent C fibres, are much less significantly affected. Our findings thus fail to resolve the question as to whether chronic clinical pain is mainly an A delta- or a C fibre-mediated phenomenon. 