1. The objective of this study was to evaluate the ability of Campylobacter jejuni to penetrate and colonise eggs from specific-pathogen-free (SPF) and heavy breeder hens, and to determine its effects on the viability of SPF embryos. 2. We detected C. jejuni in 10% of breeder hens and 20% of SPF eggs, which demonstrates the ability of the bacteria to go through the pores of eggs and contaminate the vitellus after 3 h of contact. These results indicate that there is a risk of contamination under commercial production conditions, where, after oviposition, there is contact between the egg and organic material such as faeces and blood. 3. We observed that in 80% of SPF eggs analysed, C. jejuni survived the 21-d incubation period. This positive result suggests that this microorganism was also responsible for early embryonic mortality. 4. The ability of C. jejuni to penetrate the eggs in this study suggests that serious problems may occur under natural field conditions, which may cause significant problems for producers.