The allantoic fluid of chick embryos infected withChlamydia psittaciis routinely used as a source of material for the study of the chemical and biological properties of the chlamydiae. We have examined pellets recovered from this allantoic fluid by low- and high-speed centrifugation, as well as high-speed pellets which had been stored at −70 °C, and we find that all of the pleomorphic forms of the chlamydiae are present in these materials. The reticulate bodies and large intermediate bodies are always seen to be morphologically damaged in that their cell envelopes are modified and in that they are distended and occasionally 'leaky.' No morphological evidence of damage was seen in small intermediate bodies or in elementary bodies in any of the materials which were examined. Thus the chlamydial population recovered from the allantoic fluid of infected chick embryos has been modified by selective damage to the least-condensed particles. We propose that the release of lysosomal enzymes from the host cell may coincide with the release of the chlamydia and that these enzymes may be responsible for this selective damage.