Starting from a discussion of known direct dynamic hot-wire probe calibration methods a calibration technique is described, by which the directional sensitivity of the probes is employed to determine the amplitude and phase response. Results obtained by this method indicate that an alteration of the dynamic response of hot-wire probes (constant-temperature mode) can occur for frequencies about 1 Hz, depending on the length-to-diameter ratio of the wire and the air velocity. Estimations of the energy balance of the hot-wire illustrate that the observed frequency response alteration is probably caused by the heat conduction end losses of the wire.