The main goal of prevention and health care for elderly people is optimizing 'quality of life'. Frail older persons have limited reserves and are therefore at an increased risk of a decline in health, which may lead to dependency and disability. This thesis focuses on the health-related effects of physical exercise and nutrient dense foods among non-institutionalized frail older people. First, criteria for identification of frailty were investigated using prospective cohort data. It was concluded that physical inactivity in combination with weight loss seems a practical and inexpensive screening criterion to identify functionally vulnerable persons among non-institutionalized elderly. Second, the results of a 17-weeks randomized controlled trial on a specific exercise and nutritional program in 217 frail, independently-living elderly (aged 67-96) are presented.The exercise program proved of benefit for functional status and immune response. Performance on 7 functional tests had significantly improved (+8%) in trained compared to non-trained subjects (-8%). The beneficial effect on the sum score of 7 fitness tests was also significant but smaller. Cellular immune response was measured by the delayed-type hypersensitivity skin test response against 7 recall antigens. The number of positive responses declined in non-exercising subjects (-26%) compared to an unchanged responsiveness among exercising subjects. Effects on self-rated disabilities, psychological well-being and self-rated health could not be demonstrated. Seventeen weeks of consumption of micronutrient enriched foods at physiological doses (25-100% of the RDA) did not affect functional status, cellular immune response or psychological well-being.In conclusion, exercise programs can be developed which are effective in preventing, slowing down or reversing the age-related decline in physical functioning and cellular immune response. Moreover, subjects highly appreciated the exercise program and the majority favored continuing program ...