We report on the conduct and the results of an experiment that investigates the program comprehension differences between event-driven and object-oriented programming styles. A group of novice programmers were asked to comprehend two isomorphic programs and answered a series of five questions on each of the programs. Each question was to address one of five knowledge categories that together formed a complete mental representation of the two programs. Subjects performed badly on recalling the elementary operations knowledge in both styles. They performed very well in the data flow, control flow, function and state knowledge categories for both styles. Subjects were not significantly better in the last four categories indicating that the comprehension of event-driven and object oriented styles have a lot in common. A comparison of these results with the results of earlier studies, which compared procedural and object-oriented styles, indicates that procedural style is furthest away amongst the three styles. The results are discussed in terms of relevance to the theory of program comprehension.