It is extremely useful to define a rapid and accurate method for identifying homozygous and heterozygous transgenic animals prior to setting tip breeding programs for transgenic colonies and in experiments in which gene dosage effects could have a functional impact. Southern-blotting is a means of identifying zygosity but Such a method is time consuming and produces a high level of ambiguous results. Some years ago, we described the rapid, precise, non-ambiguous, and high-throughput identification of zygosity in transgenic animals by real-time PCR. This technique allows us to make a clear-cut identification of transgenic rats, transgenic mice, and double-transgenic pigs. Since 2002, however, several authors have made improvements to this method. The following paper describes the case with which zygosity is determined using real-time PCR.