In two patients with Whipple's disease a variety of abnormalities were found in the testis. In both there was a thickened tunica albuginea containing macrophages filled with Schiff-positive bacilli, and both exhibited Whipple bacilli alone or in small clumps within the tunica media of the testicular arteries. One patient had focal inflammatory lesions among the Leydig cells. The most prominent abnormality in each was the abundance of Whipple bacilli within the epithelium of the seminiferous tubules. Some of these bacilli (which were free rather than within macrophages) appeared to be being shed into the tubular lumen; there was no associated inflammation. In some areas macrophages filled with bacilli appeared to migrate from the arterial adventitia toward the seminiferous tubules. Potential significance of these findings is discussed relative to a variety of testicular and prostatic diseases, as well as the possible (and arguable) relationship to the acquired immune deficiency syndrome.