The three major allelic variants of the mannose-binding lectin gene are responsible for structural defects leading to immune deficiency. The corresponding mutations are all located within exon 1 and result in amino acid substitutions in the collagenous region of the protein, which is involved in the oligomerization process. We have developed a simple and efficient strategy that permits simultaneous genotyping of these known allelic variants of the MBL gene by means of a single polymerase chain reaction (PCR) reaction followed by a denaturing gradient gel electrophoresis (DGGE). In addition, this procedure also allows for screening novel alleles due to mutations located elsewhere in the analyzed segment of the gene. During this study, we identified a previously undescribed nucleotide change in exon 1 at codon 44.