Chicken eggs have been used as an experimental tool since the 1880s. Further development led to the identification of the chorioallantoic membrane (CAM) as an easily accessible, highly vascularized, non-innervated anatomical structure suitable to address a broad spectrum of scientific issues. The CAM is an extraembryonic membrane that develops during the embryonic development of the chicken. Motivated by ethical concerns regarding the Draize rabbit eye test, the CAM assay was identified as an alternative method in toxicological research. The reasonable use of the CAM assay is considered a refinement of animal experiments, as it contributes to the minimization of pain and suffering according to the ethical obligations to reduce, refine, and replace (3Rs) animal usage in research.

The CAM assay is now an increasingly popular model for versatile in ovo experiments because of its low cost, simple experimental conditions, and broad spectrum of applications. It is widely used for the analysis of angiogenesis, biomaterials research, toxicology, wound healing, tumor development, and metastasis. The high density of blood vessels in the CAM creates an ideal milieu for tumor growth, xenotransplantation of tissue, study of angiogenesis, and the evaluation of biomaterials.

The goal of this Methods Collection is to cover the broad range of applications of the CAM assay and represent the versatile potential of this method for different scientific research questions. The CAM assay offers the opportunity to bridge the gap between in vitro experiments and in vivo experimentation in rodent animal models.