Since iron-binding proteins in serum and external secretions inhibit growth of certain microorganisms, the effect of lactoferrin on growth of Candida albicans was determined. The iron-unsaturated protein markedly impaired replication of the yeast, and the growth-inhibitory property was lost when lactoferrin was saturated with iron. The content of lactoferrin in parotid fluids and leukocytes from patients with chronic mucocutaneous candidiasis was measured and compared to that of normal subjects. By immunofluorescence, lactoferrin was localized in the nuclei of band forms and mature polymorphonuclear neutrophiles. There were no differences in the distribution of lactoferrin in leukocytes from patients or controls, and the mean concentrations of lactoferrin in parotid fluids from the two groups were not different. © 1971 by the University of Chicago.