<i>MANSONELLA ozzardi</i>is a human filarial parasite whose distribution is limited to areas of South and Central America and to the West Indies. In the case of other filarial parasites, brief residence in or travel to endemic areas usually does not eventuate in detectable microfilaremia. For example, of more than 10,000 American military personnel with symptomatic evidence of filarial infection with<i>Wuchereria bancrofti</i>while stationed in the Pacific during World War II, fewer than 20 had detectable microfilaremia, and this was usually transient and of low levels.<sup>1</sup>In the case reported here, an asymptomatic man with only brief exposures in endemic areas during Caribbean vacations was found to have persistent<i>M ozzardi</i>microfilaremia. The patient was a regular blood donor, and microfilaremia was initially detected on a blood smear examined at the time of blood donation. <h3>Report of a Case</h3> A healthy 46-year-old man periodically donated blood at a