We worked out TTR values in patients receiving warfarin treatment in Abashiri-Kosei General Hospital. The patients were divided into two groups - those with satisfactory TTR values and those with poor TTR values - and associations between patient factors and average dosing interval were examined in the two groups. A total of 178 patients joined this study. The average TTR value worked out at 65.1±24.8%. It was found that the average TTR value for those patients aged at 70 and above came to 72.7±21.4%, which was significantly high as compared with 51.06plusmn;24.6% for those under 70 years of age. When the average TTR value was calculated after the optimal PT-range for the group of those below the age of 70 was changed from 2.0～3.0 to 1.6～2.6, it rose from 51.0% to 74.9%. These findings made it clear that PT-INR, regardless of age, was under control within the range from 1.6 to 2.6 in this hospital in accordance with the results of the J-RHYTHM Registry analysis.