A new method of measuring vertical dislocation of the C1 and C2 vertebra in rheumatoid arthritis is presented based on the distance from the lower end plate of C2 to the palato -occipital or McGregor 's line. In a normal material the distance was found to be 34 mm or more in men and 29 mm or more in women. A value below these limits should be regarded as vertical dislocation. In the same normal material the value according to the McGregor method was found to be 9 mm or less in both sexes. In a combined material consisting of healthy individuals and patients with rheumatoid arthritis a good correlation between the two measurement methods was found. The new method has the advantage of giving a measurable value also in cases with advanced dislocations and an undiscernible dens and of giving a correct value in cases with erosions and destruction of the dens.