I determined whether transovarial passage of Lyme disease spirochetes occurred more efficiently in Ixodes scapularis Say fed on reservoir-competent dogs. Unlike deerfed ticks, spirochetes are not diminished in dog-fed ticks, and significantly higher transovarial infection rates have been reported for the latter. Females of field-infected I. scapularis (North Salem strain) were used to induce experimental Lyme disease in specific pathogen-free dogs as part of another study. Seventy-four (48 of 65) percent of the females examined were infected with spirochetes, and larvae from infected females were tested for Borrelia burgdorferi within 1 mo of eclosion. No spirochetes were found in 14,700 larvae (225 larvae per female [n = 12] and 750 larvae per female [n = 16]) examined individually by fluorescent antibody (FA) tests or in triturated larval suspensions (approximately 1,500 larvae per female (n = 20]) examined by FA and polymerase chain reaction. Larvae remain an unlikely source of B. burgdorferi infection in the peridomestic setting because transovarial transmission is highly inefficient in I. scapularis.