A guide wire (1) for use with a catheter for accessing a remote site in the venal or other system of the body of a human or animal subject comprises a core wire (2) extending from a proximal end (5) to a distal end (6). The core wire (2) terminates at the distal end (6) in a distal portion (16) which is of rectangular transverse cross-section defining a pair of opposite major surfaces (18,19) and minor surfaces (20,21). The distal portion (16) also defines a central major plane (24) which lies between the major surfaces (18,19) and bisects the minor surfaces (20,21), and a central minor plane (25) which lies between the minor surfaces (20,21) and bisects the major surfaces (18,19). An alignment portion (27) for aligning the distal end (6) with a branched vessel of the vascular system is formed in the distal portion (16) by bending the distal portion (16) in the central major plane 24 to form a curved portion (28) from which the alignment portion (27) extends, the curved portion 28 and the alignment portion 27 lying in the central minor plane 24. By bending the distal portion (16) in its central major plane, the column strength of the guide wire (1) is such as to minimize the danger of buckling of the distal portion in the central minor plane (25).
