The neutrophils in 2 patients with atopic disease were studied. Ultrastructurally, a number of abnormal azurophilic granules (AG) with low electron-density (Case 1) and secondary lysosomes with "myelinoid membranes" figures (Case 2) were found. Myeloperoxidase (MPO) and acid phosphatase activity were detected by light cytochemical techniques, and showed significantly low values. The deficiency of MPO and abnormal distribution of AG were also demonstrated by electron microscopic cytochemical technique. The neutrophils from the parents revealed changes similar to the patients. This study suggests that since genetic partial deficiency of neutrophil AG enzymes existed, the phagocytosed substances were only partially degraded, leading to accumulation of substances with antigenicity, and became trigger event of atopic disease.