Restriction fragment length polymorphism (RFLP) of human mitochondrial DNA (mtDNA) was analysed in 35 placentas from Korean (Seoul) population with 5 restriction endonucleases (HpaI, HincII, EcoRI, HindIII, StuI), without using Southern blotting analysis and the end labeling method. Among these restriction enzymes, HpaI and HincII showed at least one atypical cleavage pattern. Digestion patterns with HincII and HpaI were relatively polymorphic, while the others were monomorphic. The observed restriction enzyme morphs were classified into 6 types of distinct cleavage patterns. By pairwise comparison of each restriction type, the average number of nucleotide substitutions per nucleotide site (δ) was estimated at 0.00433, which agreed with the values obtained from other human populations in previous studies. The present data suggested that the Korean population conceals a high degree of mt DNA diversity.