Radiographic bone level changes over 2 years were assessed by 1 absolute and 2 relative techniques in a group of 180 subjects (age 18-68 years, mean 46.7). The absolute technique measured the CEJ-AC distance (mm). The Schei and Björn techniques employed rulers which expressed the alveolar bone level as a % of the root and tooth length, respectively. The applicability and readability of the 3 techniques were compared and their interrelationship evaluated. The absolute technique showed significantly better readability than did both the relative methods (p less than 0.0005), while the Schei technique exhibited the highest ability in detecting the radiographic change in bone level. The correlation between the measurements of bone level change made by the absolute and Schei techniques (r = 0.87) was far better than that between the other techniques (r = 0.56, 0.59).