Ivermectin (or Mectizan trade mark ) is widely used by onchocerciasis and lymphatic filariasis control programs worldwide. Generally, Mectizan trade mark is both safe and well tolerated. An exception to this general pattern is in some areas co-endemic for Onchocerca volvulus and Loa loa, where a number of severe adverse reactions to Mectizan trade mark have been noted in L. loa infected individuals. The vast majority of these severe adverse events have occurred in Southern Cameroon. This suggested the hypothesis that the parasites endemic to Southern Cameroon might form a distinct population that exhibited a phenotype of eliciting severe adverse reactions in Loa-infected individuals upon Mectizan trade mark exposure. To test this hypothesis, the DNA sequences of three potentially polymorphic loci were compared among L. loa parasites from Southern Cameroon and other endemic foci in Sub-Saharan Africa. Analysis of these data suggested that parasites from Southern Cameroon were at least as genetically diverse as those from other foci. Furthermore, no polymorphisms were noted that were unique to and shared among the parasite isolates from Southern Cameroon. Although a limited number of parasite isolates were tested, these results do not appear to support the hypothesis that L. loa parasites from Southern Cameroon represent a unique, genetically isolated population.