A leak detecting apparatus (1) for detecting a leak and determining the size of the leak in a suture repaired site (5) of a hollow organ (3), for example, a stomach, in a cavity (7), for example, the peritoneal cavity of a subject comprises a first insufflator (12) for insufflating the hollow organ (3) with a first gas, and a second insufflator (14) for insufflating the cavity (7) with a second gas. A gas detector (18) is provided for detecting the concentration of the first gas in gases exhausted from the cavity (7) through a communicating conduit (35). A flow meter (25) monitors the flow rate of the first gas to the hollow organ (3). First and second pressure sensors (15) and (16) monitor the static pressure of the first and second gases in the hollow organ (3) and the cavity (7), respectively. The apparatus (1) is operable in a first mode and a second mode. In both the first and second modes of operation a microprocessor (50) controls the second insufflator (14) for maintaining the pressure in the cavity (7) at a relatively low predefined pressure, and the first insufflator (12) for maintaining a constant predefined pressure differential between the pressures in the hollow organ (3) and the cavity (7) of approximately 7mmHg. In the first mode the microprocessor (50) determines the size of the leak as a function of the pressure differential and the concentration of the first gas in the exhaust gases. In the second mode of operation the microprocessor (50) determines the size of the leak as a function of the pressure differential and the flow rate of the first gas to the hollow organ (3) with the hollow organ (3) sealed apart from the sutured site (5). <；Figure 1>；
