The study target accrual is at least 20 subjects who complete collection of blood, oral, rectal and genital specimens through 2 weeks after the rAd5 vaccination. To account for potential discontinuations from the study, enrollment may include up to 36 HIV-uninfected adults, ages 18-50 years old that are HIV vaccine-naive and adenovirus serotype 5 (Ad5) antibody negative at screening; males must be fully circumcised.