Little is known about cardiorespiratory fitness and aerobic exercise training in older adults with Alzheimer's disease (AD). The purposes of this article are to describe the change in cardiorespiratory fitness after 2 months of aerobic training and the feasibility of aerobic training in 4 men with moderate-to-severe AD. A one-group, pretest-posttest test design was used to measure cardiorespiratory fitness using symptom limited, graded cycle ergometer testing. In exit interviews, participants and spouses identified exercise facilitators and barriers. The results show that cardiorespiratory fitness increased in 2 participants with moderate AD but decreased in 2 with severe AD. Participants showed great variability in exercise progression and doses actually delivered. In conclusion, older men with moderate-to-severe AD can engage in aerobic training. Two months might be better used as the adaptive period for longer duration aerobic training, such as a 6-month program. Suggestions and implications for future exercise research in AD are detailed.