Mannose-binding lectin (MBL) levels in the plasma of humans are highly variable. The level is influenced by gene mutations in exon1 and the promoter. Here we describe the distribution of three point mutations linked with a deletion in the MBL gene promoter in populations of Central Africa, Thailand, and Papua New Guinea. Among African children we find 20% with the wild-type allele, 53% are heterozygous, and 27% are homozygous for the mutation, In Thailand we find 65% with the wild-type allele, 33% are heterozygous, and 2% are homozygous for the variant. In Papua New Guinea the polymorphism is not found. The occurrence of the mutation was associated with MBL levels in the plasma (P = 0.043). Oligonucleotides derived from the variant promoter regions bind proteins differently according to their DNA sequence. The binding of proteins can be influenced by induction with interleukin-6.