Research has shown that many antihistamines produce sedative effects as well as impair psychomotor performance. Performance testing of antihistamines, however, has not produced reliable evidence that there are behavioral effects at therapeutic dose levels. Therefore, the objective of this research was to determine whether a complex cognitive and motor task (memory search and tracking combination) showed a performance deterioration under the influence of two antihistamines (benadry| and hismanal) and to determine if the chosen task was of sufficient sensitivity to register decrements in performance at therapeutic dose levels of either of these two antihistamines. Thirty male subjects were divided into five groups of six subjects each. Each of the five groups was tested one day per week for three consecutive weeks. All Subjects received all three treatments (two antihistamines and a placebo) over the course of the test sessions. Order effect of the drug administration was counterbalanced. Analyses of variance showed that benadryl impaired performance on both components of the task as expected. Performance under hismanal did not vary significantly from the placebo. Post hoc testing further revealed an expected significant effect of benadryl three hours following ingestion for three out of four dependent variables. Again, hismanal effects did not vary significantly from those of the placebo. Hence, the memory/tracking combination task registered an expected performance impairment by benadryl which implies sufficient sensitivity of the task to register decrements. Also, hismanal displayed an expected lower incidence of behavioral effects as measured by response time and tracking error, which implies hismanal's usefulness in facilitating normal performance. / Master of Science