A catheter for use in neurosurgery, and a method of positioning neurosurgical apparatus. The catheter has a fine tube arranged for insertion into the brain parenchyma of a patient with an external diameter of not more than 1.0 mm. The catheter and method may be used in stereotactically targeting treatment of abnormalities of brain function, and for the infusion of therapeutic agents directly into the brain parenchyma. This is advantageous when a therapeutic agent would have widespread unwanted effects which could be avoided by confining the delivery to the malfunctioning or damaged brain tissue.