The kinetoplast DNA (kDNA) from promastigotes of Leishmania responsible for Old and New World cutaneous and visceral disease was characterized to determine if species and strains causing similar or different diseases could be identified. Restriction enzymes were used to digest kDNA into fragments that were separated into characteristic banding patterns after electrophoresis in agarose or linear gradient polyacrylamide gels. Hybridization was conducted with a 32P-kDNA probe and kDNA fragments transferred from agarose gels to nitrocellulose paper. Leishmania species causing cutaneous diseases in the New and Old Worlds all had different kDNA digest patterns. Visceralizing Leishmania from the New and Old Worlds also had different kDNA restriction fragment patterns although Leishmania donovani parasites with similar fragment patterns were isolated from several humans from central Kenya. Nucleotide sequences were shared among kDNA networks from L. donovani, Leishmania d. chagasi, Leishmania d. infantum, Leishmania tropica, and Leishmania major as determined by hybridization with a 32P-kDNA probe from L. donovani. However, no hybridization was detected between the L. donovani 32P-kDNA probe and kDNA from Leishmania aethiopica or Leishmania braziliensis panamensis. Leishmania characterization results for the same isolates from the published literature were compared and kinetoplast DNA analysis was found to be one of the most sensitive procedures for species and strain identification.