The polymorphism of human mitochondrial DNA (mtDNA) was studied in 118 unrelated Greeks (from northern Greece) using total blood cell DNA and the restriction enzymes HpaI, BamHI, HaeII, MspI, AvaII, and HincII. One new morph was identified for MspI (named MspI morph 18Gr) and is the result of a mutation in a previously thought monomorphic site at 104 bp. HpaI morph 1 was detected for the first time in a European sample. Also, AvaII morph 13 was observed in Greece in a frequency higher (5.93%) than that found in any other population. Eighteen mtDNA types were identified, three of which are new [86-2 (1-3-1-4-9-2), 87-2 (2-3-1-1-13-2), and 88-2 (2-1-1-18Gr-1-2)] and can be derived from already known mtDNA types by single restriction site changes. Type 57-2 (2-3-1-4-13-2), which had been previously characterized as "Italian," was found with higher frequency (4.24%) in northern Greece. The calculation of genetic distances and chi-square values through Monte Carlo simulation shows that the Greek sample does not differ from the Italian sample.