In order to determine the relative efficiency of a Ge(Li) detector in the region of 8O–1000 keV, measurements of a standardized166mHo solution were performed. The radioactivity concentration of the166mHo solution was determined by measurements of a133Ba reference standard. The total number of calibration measurements was 120. The influence of experimental conditions such as sample manufacture, absorption of the vessels, source positions and dead time, on the accuracy of the measurements, was considered. The observed spectra were analyzed by a simple programme. In comparison with other calibration nuclides, the advantages of the multigamma-ray nuclide166mHo are simple manufacture, large half-life and homogeneous distribution of gamma-rays with absolute intensities greater than 5% in the region of 8O–1000 keV.