Genetic polymorphisms in neuronal nitric oxide synthase (NOS1) and calmodulin-dependent endothelial NOS (NOS3) genes are known to influence the course of allergic respiratory disorders. We investigated the role of NOS1 -84 G-->A and NOS3 -786 T-->C, 894 G-->T and 27 base pair (bp) repeat polymorphisms in 125 patients suffering from asthma and/or rhinitis and monosensitized against Dermatophagoides pteronyssinus (Dpter) and 111 controls from Algeria. We found a higher frequency of the -786 C NOS3 allele in patients than in controls [corrected P value (Pc) = 0.04], especially in female cases (Pc = 0.02) and that the 'ab' genotype of the 27-bp polymorphism was significantly associated with specific immunoglobulin E production against Dpter (P = 0.006). This study brings further support for the participation of NOS3 gene polymorphism in the pathogenesis of respiratory allergic disorders.