This paper describes observations of the reliability of the ionospheric HF communication channel within and close to the northern auroral zone. Automatic equipment has been developed to measure reliability and virtual reflection height as a function of frequency in an hourly cycle. Measurements have been made over two propagation paths within Norway. The data show diurnal and seasonal variations as well as dependence of the measured parameters on geomagnetic conditions. The observations have been compared with predictions obtained from the Ionospheres Communication Enhanced Profile Analysis and Circuit Prediction Program (ICEPAC) prediction code. This code includes a model of the high-latitude and polar ionospheres and their dependence upon geomagnetic disturbances. The results of the comparison show that ICEPAC represents an improvement over previous codes but that transmission losses are not properly included. ¿ American Geophysical Union 1994