Selected immunologic functions were assessed in 14 patients with the Shwachman syndrome. Nine patients were neutropenic and four had low levels of IgA or of IgM. Neutrophil mobility was significantly defective in the group of patients as a whole (in 12 it was below the lower limit of normal) and in their parents. No other consistent abnormality in immunity was found. These results suggest that the defective neutrophil mobility is a feature of Shwachman syndrome which may contribute to the vulnerability of these patients to frequent infections. The defect appears to be a primary genetic one, inherited as an autosomal recessive characteristic consistent with the assumed inheritance of Shwachman syndrome.