Field voles are common in Britain and across Europe where they may show regular fluctuations in population every 3-4 years. In some countries they are pests of agriculture and particularly of forestry. These voles are induced ovulators and, while their reproductive physiology is fairly well understood, little is known of their reproductive behaviour and especially of their acoustic communication. The present study has shown that in heterosexual encounters adult voles emit ultrasonic calls during a range of behaviours, as has been found in several other rodents. For example, male mice of different strains are known to emit 70 kHz ultrasonic vocalizations as part of their courtship behaviour, and rats emit 50 kHz pulses. In Microtus agrestis, the nature of the calls varies particularly in the amount of frequency modulation. The frequency ranges from 20 kHz to 80 kHz, with an average at 35-40 kHz, and the male seems to be the main emitter. In heterosexual encounters between sexually naïve animals both sexes call, but calling appears to be modified by sexual and parental experience, as sexually experienced males emit longer and wider calls than sexually naïve males, and sexually experienced females do not emit any ultrasonic pulses when presented with an anaesthetised male (also sexually experienced), as sexually naïve females do. The environment in which the animals meet also affects ultrasound emission: the calls emitted by pairs in the male's home cage were longer and of broader-bandwidth than those emitted in the home cage of the female. The effect, on the emission of ultrasonic pulses, of sexual and parental experience as well as the effect of different environments will be illustrated. The relationship between calls and the different types of behaviour and the effect of these calls on the recipients are currently being investigated.