Mannan-binding lectin (MBL), an important component of innate immunity, binds to a range of foreign antigens and initiates the lectin complement pathway. Earlier studies have reported high plasma MBL levels in allergic patients in comparison to healthy controls. In view of varied plasma MBL levels being determined by genetic polymorphisms in its collagen region, we investigated the association of single nucleotide polymorphisms (SNPs) in the collagen region of human MBL with respiratory allergic diseases. The study groups comprised patients of bronchial asthma with allergic rhinitis (n = 49) and allergic bronchopulmonary aspergillosis (APBA) (n = 11) and unrelated age-matched healthy controls of Indian origin (n = 84). A novel intronic SNP, G1011A of MBL, showed a significant association with both the patient groups in comparison to the controls (P < 0.01). Patients homozygous for the 1011A allele showed significantly higher plasma MBL levels and activity than those homozygous for the 1011G allele (P < 0.05). The 1011A allele also showed a significant correlation with high peripheral blood eosinophilia (P < 0.05) and low forced expiratory volume in 1 s (FEV(1)) (P < 0.05) of the patients. We conclude that the 1011A allele of MBL may contribute to elevated plasma MBL levels and activity and to increased severity of the disease markers in patients of bronchial asthma with allergic rhinitis and ABPA.