During the period 1975—1980 in Bulgaria 6 TLD postal dose intercomparisons including all teletherapy units have been performed. LiF powder TLD-100 and a Harshaw TL analyser model 2000 have been used. The fading effect and the accuracy of the dose measurements for60Co gamma rays have been investigated preliminarily. The fading is below 1% for 30 days. The sensitivity of the reading equipment has been investigated using the mounted check light source. By means of a statistical analysis it was determined that the relative uncertainty due to unstabilities in the sensitivity is ±0,24% at confidence level P = 0,95 for a set of 10 successive check source readings. In the same manner the relative uncertainty of the dose measurements using one TL detector (4 measurements) was determined to be ±1,6% at P = 0,95. The intercomparison performance method is described and the results from the six intercomparisons are presented.