COMPLETE conltrol of leptospirosis in man depends on the elimination of the infection in carriers. After acute or, frequently, inapparent infections in domestic and wild animals, the organisms become established in the kidneys and may be shed with urine chronically. Urinary shedders of leptospires are primary vectors: the infection passes to other animals and to man by direct or indirect contact with infected urine. Preventive measures have most often been aimed at the leptospire outside the body of its host (1). In the past, control methods pursued the destruction of the leptospire by chemical agents, heat, or desiccation; or they were designed to prevent the leptospire from gaining access to the susceptible host by ratproofing, confinement, or protective clothing. At present, immunization of susceptible populations and elimination of carriers by antibiotic treatment are being emphasized. In some instances, however, the best means of control may lie in the prevention of contact. For example, in the United States, most outbreaks of leptospirosis in humans (primarily in children and young adults) have occurred as a result of swimming in stagnant pools or streams contaminated by infected urine from animals. Notices placed in schools and service establishments might prove effective in warniing swimmers of their risk.