In order to study the relationship of certain syntactic variables to reading comprehension difficulty, 80 high school seniors were asked to read and then paraphrase 16 types of relative clause sentences to demonstrate their understanding of the sentences. Each sentence included one independent clause and one relative clause, and each lacked any semantic clues. The effects of relative clause position and relative clause structure were substantial and consistently stronger than independent clause structure, although all three were found to affect comprehension scores. Easier sentence comprehension occurred when the relative clause followed the independent clause, when the independent clause was active rather than passive, and when, in relative clause structures, the agent was mentioned first and the verb was passive. Comprehension difficulty related less closely to the use of the passive verb form than to the word arrangement in particular passive constructions. Relative infrequency of use also may have contributed to the comprehension difficulty of some types of clauses. (Author/MF)