This study's first objective was to apply Ajzen's theory of planned behavior (TPB) in the context of automobile child restraint device use to identify determinants of that behavior. A second objective was to test two specific hypotheses regarding the predictive role of perceived behavioral control: (a) Its inclusion should increase the proportion of variance already explained in intention by the attitudinal and normative components included in the theory of reasoned action; and (b) given the behavior under study, a model in which perception of behavioral control's influence on behavior is entirely mediated by intention, should fit the data. Subjects (N= 590) were parents driving with their 3- to 5-year-old children intercepted while entering or leaving parking lots of different public settings. The behavior of interest, child restraint device use, was rated by two independent observers. A self-report questionnaire assessing all constructs of Ajzen's model was given to the parent, who was instructed to return it by mail. Data were analyzed using LISREL VII. Results showed that perceived behavioral control and, to a lesser extent, attitude, emerged as the main determinants of behavioral intention which was itself predictive of child restraint device use. In addition, both hypotheses regarding the relation between perceived behavioral control on the one hand and intention and behavior, on the other, were supported. Discussion centered first on the mechanism through which perceived behavioral control exerts its influence, and second on the implications of the present results for the theory of reasoned action as well as for the theory of planned behavior.