An ion frictional heating event was observed by the EISCAT facility at 22:00 UT on 5th September (1989). The Sheffield University plasmasphere and ionosphere model has been used to investigate this event. A closed subauroral tube of plasma is considered in the model which has been developed to include temperature anisotropy in the NO+ as well as in the O+ ion populations. During the event the O+ temperature distribution becomes more anisotropic than the NO+. This means that in the F region the temperature of the NO+ ions parallel to the magnetic field is substantially greater than the temperature of the O+ ions parallel to the magnetic field. The model predicts that the ion composition in the F region becomes more molecular during the event. At an altitude of 300 km the composition changes from almost 100% O+ ions to 70% NO+ ions. To account for the change in ion composition which is not considered in the standard EISCAT analysis the EISCAT data were reanalysed using the ion composition predicted by the model. To compare with the measured ion temperature an average ion temperature was calculated from the model O+ and NO+ distributions. An additional heat source was introduced to enhance the model electron temperatures. There was then reasonable agreement between the modelled and measured parameters. Similar observational and model results were obtained for the ion frictional heating event observed at 21:00 UT on 9th May (1982).