Abstract Foetal behaviour in domesticated animals constitutes a novel subject of ever-increasing interest to applied ethologists. The use of an ultrasonic approach in a study of quantitative equine foetal movement is reported here on 62 subjects. Mares were examined with an intra-pelvic transducer probe relaying a signal of high frequency and low intensity. Sonic evidence of foetal movement took the form of very short, sharp and characteristic increases in pitch. Foetal kinesis was found throughout the greater part of pregnancy and, with gestational progress, different features of foetal kinesis became recognisable. Simple, singular movements were of common and quite regular occurrence and could be detected from the third month of age onwards. Such movement maintained a fairly constant daily incidence, averaging 9 movements per 10 min. Movements of greater complexity emerged in the kinetic behaviour of the more mature equine foetus. Co-ordination in the distribution of complex foetal movements led to their grouping into active phases. Mass activity in lengthy phases occurred in the pre-partum stage of gestation. The peak of foetal activity occurred 3 days prior to parturition. Phases of no detectable activity were encountered in foetuses of all ages, but were of greatest duration in older individuals. The simple foetal movements evidently represent a form of foetal exercise. This exercising is analogous to isometrics. This form of activity is probably required to ensure the satisfactory muscular development of the foetus and the function of skeletal joints. The demands of the adaptive process in the new-born foal are well known and it is now clear that much of the success of this adaptation is dependant on the preceding foetal behaviour described here. From this study is it clear that the foetal activity which requires to be invested in the attainment of the correct posture for birth is considerable. Estimates indicate that 5 000 to 10 000 foetal movements are required for the righting and postural reflexes to be completed which represents a very significant quantity of foetal work.