Twenty-eight patients with defective neutrophil mobility were classified, largely on results of parent values, into primary (17)--mainly Shwachman's syndrome--and probable secondary (11). They presented with frequent infections and/or allergy and these symptoms were essentially similar in both groups. Neutropenia was virtually confined. to the patients with Shwachman's syndrome. Diagnoses associated with secondary neutrophil mobility defects included hydrocephalus with shunt, cystic fibrosis, and immunoglobulin deficiency. The neutrophil mobility of nearly nearly all the patients studied increased when levamisole was added in vitro, but there was no clear evidence of clinical benefit when patients were given the drug.