Abstract
Small pieces of ovine hydatid cysts devoid of brood capsules and protoscoleces, and half or quarter pieces of secondary sterile murine cysts of equine origin failed, over a six-month period, to regenerate when passaged into the peritoneal cavity of BALB/c mice. The majority of similar pieces placed in microdiffusion chambers prior to insertion into mice also failed to regenerate, suggesting that the passage of cyst pieces may not be totally reliable in the assessment of the viability of germinal layer tissue after chemotherapy.