Abstract: A method and apparatus for leak testing a sealed package having at least one flexible wall portion and a sealed flange wherein at least one flexible wall portion of the package spaced from at least a seal-exposing edge of the sealed flange is gripped and pulled outwardly from the package to stress the package in tension while at least the seal-exposing edge of the sealed flange is exposed to a gas pressure equal to or greater than atmospheric pressure. The reaction of the sealed package to the stressing is then detected. The method and apparatus are useful for testing retort or aseptic pouches, cups and multi-layered trays with heat sealed lids, etc., with or without head space. Leaks in the seal and also in areas adjacent the seal can advantageously be detected quickly and with a high degree of reliability.