This peripheral blood smear derived from one of our patients who previously worked in tropical West Africa. It shows a prominent microfilarial or larval form of Loa loa. The larvae are carried by Chrysops flies. When bitten by the fly, a host is infected by the larvae which migrate to the subcutaneous tissues and muscles where they develop into adult forms a year later. The clinical features of loiasis include subcutaneous swellings and if the eyes are involved, irritation and impaired vision. The adult worms, macroscopic in size, are troublesome when passing through the orbital conjunctivae or across the bridge of the nose. An adult worm was recovered from this patient's eye by a local ophthalmologist. Photograph: John K. Scariano, University of New Mexico Department of Pathology, courtesy of Cecily Yee and Tri-Core Laboratories.