Abstract: An ultrasonic insertion flowmeter (100) is disclosed having a probe (101) which is adapted to be inserted into a duct, the probe having at least first and second ultrasonic transducer means, the probe (101) being adapted to measure the transit time difference of an ultrasonic pulse along a first path and a second path, the difference in transit time for signals along the two paths enabling the flow rate to be measured. Preferably, the probe takes measurements in both the forward and reverse directions along each path, and is adapted to rotate after initial insertion from an insertion position to a measurement position, whereafter the probe (101) may be drawn up against a wall of the duct so that alignment of the probe within the duct is readily achieved.