Seventeen children previously judged to be good or poor responders to methylphenidate (Ritalin) were tested on sensory integrative measures while in the off-drug state. The tester was unaware of the children’s drug response category. Results showed that children who were poor responders to Ritalin showed prolonged scores on and an adverse reaction to the Southern California Postrotary Nystagmus Test and had poorer equilibrium reactions and lower double tactile stimuli scores than the children judged good responders to Ritalin. These findings suggest that it might be possible to identify good and poor responders to Ritalin before the medication is given, something not previously thought possible. The current method for making this distinction is through a drug trial. These findings also indicate that there are at least two discernible types of hyperactivity associated with attention deficit disorders (ADD) that are theoretically related to differences in vestibular processing: one related to underaroused or overinhibited lower brain centers, and another related to deficient inhibition from higher brain centers. The good responders to Ritalin appear to be the underaroused group, the same population that responds to sensory integrative occupational therapy techniques. This implies that perhaps occupational therapy could be used to reduce the medication needs of these children.