Large electron temperature increases (~3000 K) in the ionospheric F-region, produced by powerful HF wave injection, were measured using the EISCAT incoherent scatter radar near Tromsø, Norway, on 7 October 1999. Magnetic fieldaligned measurements showed HF-initiated ion outflows reaching several hundred ms-1 at 580 km. When scanning the radar antenna from field-aligned (77.2deg southward) to vertical, the strongest heating effects were always in the fieldaligned position, irrespective of the HF beam direction which was varied. The imaged 630 nm HF-enhanced airglow also remained localized near field-aligned. Why the strongest heating effects occur for HF rays transmitted along the magnetic field is unclear.