Two experiments were conducted to investigate how event representation might operate in preschool children's understanding of the temporal terms "before" and "after." The first study, involving 3- and 4-year-olds (a total of 16 of each age) varied the arbitrariness of event sequences. Sixteen stories, each containing five events and concerning typical activities in the lives of preschool children, were used. Results indicated that, contrary to previous claims, preschool children do understand these temporal terms. The second study--involving 48 children categorized by age into groups with members 3, 4, and 5 years of age--varied the arbitrariness/logicality of event order and assessed children's comprehension and production. A new comprehension measure and two measures of production were used. Results indicated that very young children do give indications of understanding the temporal terms under conditions where event representation exists and task demands are minimal. Event representation was not found to be sufficient where task demands are great or where event representation is irrelevant to the task. Furthermore, familiarity with the basic type of event in the nonlinguistic context was shown to be insufficient to elicit the young child's knowledge of "before" and "after"; it was therefore concluded that the temporal structure of the event is an essential ingredient in supporting the child's performance. Results also suggested the need for devising very simple tasks that rely specifically on event representation in order to tap young children's knowledge of other temporal terms. (RH)