ABSTRACT. Diapausing pupae of Sarcophaga crassipalpis Macquart and S. bullata Parker reared at 20 or 25d̀C readily survive exposure to - 10d̀C for at least 25 days. In contrast, non-diapausing pupae produced by a variety of means are consistently intolerant of the low temperature. Non-diapausing pupae are not immediately killed by exposure to -10d̀C: pupae exposed to the low temperature for up to 3 days proceed with pharate adult development but ultimately die before adult eclosion. Unlike many temperate zone insects, diapausing flesh fly pupae do not require a period of chilling for induction of cold-hardiness, and the attribute of cold-hardiness cannot be separated from other features of the diapause syndrome. Some cold-hardiness is already acquired during the third larval instar: diapause-destined larvae exposed to -10d̀C are more successful in pupariating than non-diapause-destined larvae of the same age.