Two experiments were conducted on the use and combination of three cues that differentiate active from passive verbs: a form of the auxiliary "be," the morphology of the passive participle of the verb, and the case-making preposition "by." In the first experiment, 59 children aged 2.9 to 5.10 years were asked to interpret sentences with one, two, three, or no passive cues. Eight reversible action verbs were used, half of which have passive participles different from the simple past tense (homophonic) and half of which have passive participles identical to the simple past tense forms (unique). The children were asked to act out with toy animals the sentences given to them, first with intransitive practice sentences and then with the test sentences. Although it was expected that the unique passive participles would be better cues for passive than homophonic participles, no significant difference was found except in one five-way interaction of factors. The second experiment used college graduates and an almost identical procedure to determine whether the more mature children were interpreting the sentences as adults would. Results suggest that even when children interpret passive sentences correctly, they may not be processing them the way adults do. (MSE)