Embryonic stem cells (ES cells) represent a population of pluripotent, undifferentiated cells derived from early embryos that are capable of proliferating without any limitation in an undifferentiated state, and when injected into blastocysts, they can participate in the formation of all tissues. It is possible to transfect them with a gene of interest, and the resulting transgenic cell lines can also be used for production of chimeras. Before application of stem cell therapies into a human medicine, itis necessary to verify these methods with an acceptable animal model. The pig is currently used for pre-clinical applications, and therefore establishment of porcine ES cell lines is highly needed; unfortunately, no convincing ES cell lines have been produced in this species (and other domestic animals) to date. We discuss the recent advances in this field, especially oriented on possible reasons and obstacles why derivation of porcine ES cell lines is still unsuccessful.