Here we present the first report of heart rate, blood pressure, and locomotive activity of a female common marmoset (Callithrix jacchus) that was moving freely in its home cage during gestation, parturition, and lactation. We collected the data by using a miniaturized telemetry and data-acquisition system (Data Sciences, St. Paul, MN) that had been adapted for marmosets (1). The parameters were recorded continually from 12 days before to 15 days after parturition. Parturition lasted about 3.5 h, during which marked changes in heart rate, systolic blood pressure, and diastolic blood pressure occurred. To obtain control values, we again measured these parameters for 13 days during a "physiologically neutral" phase (4 months after parturition), when the female was neither pregnant nor lactating. Heart rate was 200% higher, systolic blood pressure was 25% higher, and diastolic blood pressure was 75% higher during parturition than during the neutral phase.