Throughout this study the maxillary vibrissae have been regarded as tactile organs in the sense that they convey detailed information relating to the contact or imminent contact between external objects and the face of the cat. The possible use of these hairs as a composite organ in orientation and searching behaviour, especially in the dark, is stressed. In this interpretation of the results of this study an attempt has been made to view the function of mechanoreceptive afferents in as wide a sense as possible, recognising the possibility of parallel processing of tactile information in separate functional pathways. The experimental work has been directed towards establishing the role of tactile information in the synthesis and control of motor activity by its influence on cells of the cerebellar cortex. This in itself would seem to pre-define the function of such an influence by the presumption of a purely motor operation of the cerebellum. However, in terms of the percept ion of the spatial and temporal relationships between the body and external objects the cerebellum may not act simply as a high order motor ganglion but as an integral part of a more broadly defined somatosensory system.