OBJECTIVE: To locate the source of slowness in typing movements in subjects with spastic hemiparesis and to examine whether enlargement of keys would facilitate typing. DESIGN: Experimental within-subjects design. SETTING: Werkenrode, a special school for physically disabled young children. SUBJECTS: Eleven subjects (mean age 17.1 years) diagnosed as having spastic hemiparesis, most as a result of cerebral palsy. INTERVENTIONS: Subjects made fast reciprocal tapping movements with one finger of both hands separately within a 10-second interval. Keys of 12 x 12 mm and 24 x 24 mm were used. MAIN OUTCOME MEASURES: Interkey response interval (IRI), dwell time (interval during which the key is pressed) and forces were measured. Also, the standard deviation and coefficient of variation of the variables were calculated to determine regularity of the movements. RESULTS: The impaired hand tapped slower and more irregularly and exerted less force. In addition, the duration of the dwell phase was lengthened for this hand. However, the percentage dwell time as a function of IRI was not different between hands. Enlargement of the keys shortened flight time (i.e. time in which the finger moves through the air from one key to the next) of the impaired hand, but not dwell time. CONCLUSIONS: The entire movement is slower for the impaired hand. Disturbances are not exclusively located at the inversion of the movement. With respect to keyboard design, enlarged keys and a locked repeat function of the keys may be beneficial for subjects suffering from spasticity.