It was investigated whether a deficiency of mannose-binding lectin (MBL), which binds Aspergillus species avidly in vitro, could account for chronic necrotizing pulmonary aspergillosis (CNPA), which is seen most commonly in nonimmunocompromised patients. Blood samples were obtained from 11 patients (10 white) with CNPA and were compared with blood samples from 82 white control subjects. MBL haplotype profiles were determined by polymerase chain reaction, using sequence-specific primers and sequence-specific oligonucleotide probing techniques. Seven of the 10 white patients with CNPA had MBL haplotypes that encode for low levels of the protein, compared with 25.6% of the white control subjects (P=.004). Presence of the codon 52 mutation was particularly common in patients with CNPA (P=.015), which suggests a greater involvement of this mutation.