How many markers or how many alleles per system are appropriate in zygosity testing?

Due to the development in DNA-PCR-technique more and more systems with a hi gh number of alleles have been established in twin diagnosis. Because of th eir high effectiveness in resolving of genetic questions it is not amazing that some authors have postulated the thesis that typing of 5 to 10 DNA-PCR systems can prove monozygosity. For this paper the use of different system s (conventional and PCR systems) has been tested for twin diagnosis and the observed effects are discussed.