This study evaluated whether two people with multiple disabilities who could not easily use a computer through a standard input device (i.e., mouse or trackball) would be able to improve their pointing performance using thumb poke with a standard trackball through a Dynamic Trackball-Pointing Assistive Program (DTPAP) and a newly developed trackball driver (i.e., a new trackball driver replaces the standard trackball driver, and changes a trackball into a precise thumb poke detector, and intercepts trackball action). Initially, both participants were given baseline sessions, then intervention started with the first participant. When his performance was consolidated, new baseline and intervention occurred with the second participant. Finally, both participants were exposed to the maintenance phase. Data indicated that both participants improved their pointing performance significantly with the use of DTPAP and remained highly successful through the maintenance phase. Implications of the findings are discussed. (Contains 3 figures.)