A critical evaluation of 3 years' experience using laboratory screening to detect neutrophil dysfunction is described. Neutrophil dysfunctions in patients with recurrent bacterial infections were investigated by using the following screening tests: (1) neutrophil chemotaxis towards N-formylmethionyl peptides (FMLP) and the complement fragment C5a; (2) neutrophil production of superoxide anions (O2-) in response to phorbol myristate acetate and opsonized zymosan particles; and (3) examination of May-Grünwald and myeloperoxidase cytochemical staining of peripheral blood smears. These tests were carried out in 100 patients suffering from infections and suspected of having altered neutrophil functional competence. A minority of patients was found to have well defined neutrophil dysfunction syndromes: chronic granulomatous disease (four cases), Chediak-Higashi disease (one case) and myeloperoxidase deficiency (one case). Of the remaining 94 patients, in whom infections localized to airways and/or skin predominated, 53 cases were found to have impaired chemotaxis (41 cases) or partial defects of the O2- production. Defects of chemotaxis toward FMLP and those towards both FLMP and C5a were the most frequent abnormalities. No defect was found in the other 41 patients. Moreover, impaired neutrophil chemotaxis was found in some patients with selective IgA deficiency (five cases) or immotile cilia syndrome (seven cases). The results suggest that (a) additional screening tests are required to ameliorate the efficiency of the diagnostic work-up of the patients suspected to have neutrophil dysfunction; and (b) further evaluation, also at the molecular level, should be considered at least in selected cases of non-classified neutrophil dysfunction in order to clarify diagnosis and plan rational therapeutic strategies.