We have investigated the transmission of parental mitochondrial DNA (mtDNA) in three clones of born cattle obtained by intraspecific cytoplast-blastomere fusion. Using allele-specific TaqMan PCR a low level transmission of blastomere mtDNA (DB mtDNA) into the cloned offspring was detected, thereby generating a heteroplasmic population of mtDNA. The amount of DB mtDNA was 13% and 18% in two animals of a clone which derived from a 24-cell morula and 0.6% and 0.4% in two calves of clonal origin derived from a 92-cell morula. These values are in accordance with the tendency expected for neutral mtDNA segregation that the fewer cell divisions that have occurred in the donor embryo, the higher the amount of DB mtDNA. We also found a strong decrease of DB mtDNA which was about three orders of magnitude in the third clone derived from a 52-cell morula stage. (C) 1998 Federation of European Biochemical Societies.