Previous research has shown that most antihistamines have sedative effects and can lead to deterioration of psychomotor performance. The objective of this research was to determine if two antihistamines (diphenhydramine and astemizole) administered at a therapeutic dose level will affect a subject's visual search capabilities. The results of this research indicate that astemizole did not significantly decrement a subject’s ability to visually search as compared to the performance of that same subject after ingesting a placebo. Diphenhydramine produced significantly poorer visual search results than did astemizole. / Master of Science