The orientation pulses of Natalus (Natalidae) have been recorded for the first time. These pulses are of a frequency modulated design with an initial frequency of about 85 kc and a terminal frequency of about 40 kc (roosting) or 55 kc (flying). A second harmonic component is also present. Pulses average 2.5 msec in duration. The orientation pulses of Balantiopteryx ( Emballonuridae ) are of a harmonic pattern with a slight fundamental frequency drop of 3–4 kc from beginning to end. Initially the fundamental of about 20 kc is accompanied by its second and third harmonics. These pulses average 3.2 msec in flight and are very similar to previously described pulses of Taphozous and Saccopteryx.