Objective: Despite past findings about the contribution of home care services to older users' functional ability, the effective processes and components of the services are not transparent. Such processes appear to rely on the actual use of component services of the home care program. Method: The study gathered 116 observations during 2 years concerning 49 home care service users in Hong Kong. Results: The study shows that an older user maintained better functional ability with a longer time of using a home care program in Hong Kong using the service. The time effect, in turn, was primarily due to the increased use of seven services provided by the program. Among the service components, the home-nursing services generated a unique contribution to the user's functional ability, with its prior score controlled. Conclusions: Multidisciplinary services under case management underpin an effective home care program. (Contains 3 tables.)