Rectal microbicides to prevent HIV transmission are currently being developed in the hope that someday they will be widely used to prevent sexually transmitted HIV. This study will examine variables in male rectal tissue; this information may be useful for future rectal microbicide safety and efficacy studies. The study will evaluate the differences in rectal tissue from HIV infected or uninfected males who either engage in anal-receptive sex (men who sleep with men, or MSM) or do not have anal-receptive sex.