Oestrous and dioestrous rats were observed during the initial 2 min of open-field exposure, and after a loud bell had sounded. Although defecation and ambulation showed characteristic difference between the two phases (less defecation and more ambulation at oestrus), other measures associated with emotional behaviour (latency to move from the wall, flight, and freezing to the bell) showed no differences. These findings supported Drewett's suggestion that open-field defecation and ambulation change with oestrous phase because of general metabolic changes and not as a result of 'emotionality' changes.