The amplitude and phase of subionospherically propagating VLF signals are known to be sensitive indicators of the electron density and temperature at D region altitudes. In this paper we present new observations at a station in Alaska positioned to provide measurements of VLF signals that have propagated beneath the ionospheric region heated by the high-power auroral stimulation (HIPAS) HF heating facility near Fairbanks, Alaska. Analysis of data from HIPAS campaigns conducted in fall 1992 and spring 1993 has shown that in roughly 60% of the cases analyzed, the amplitude of the 23.4-kHz signal from the NPM transmitter in Hawaii as observed in Fort Yukon, Alaska, exhibited a measurable change in amplitude with the same on/off modulation pattern as that of the HIPAS HF transmission at 2.85 MHz. In almost 70% of the cases analyzed, the same signal exhibited similar measurable changes in phase. The amplitude changes ranged from -0.2 dB to +0.5 dB, and the sensitivity of the measurement was approximately ¿0.02 dB. The phase changes ranged from -4.5¿ to -0.3¿, and the sensitivity of the measurement was typically ¿0.4¿. It is demonstrated that the phase and amplitude changes can be used as diagnostic tools to determine characteristics of the ambient electron density profile above the HIPAS facility. ¿ American Geophysical Union 1995