The distribution of transferrin phenotypes was investigated in nine populations of southwestern Japan: mainland Kagoshima Prefecture and the Nansei Islands. Populations from Tanegashima to Okinawa were homogenous in the distribution of TF C subtypes. Miyako and Ishigaki in the southwesternmost region had higher frequencies of TF*C1, and lower frequencies of TF*C2 than the seven other populations. A new TF D variant, tentatively designated TF Dama, differed in isoelectric point from adjacent variants including TF Dchi, TF Doki and TF D1. TF*Dama was found to be a new genetic marker for the Nansei Islands. Geographical clines of TF allele frequencies are also discussed.