This thesis reports the findings of an experimental study into the interpretation of subject pronouns in ambiguous intra-sentential forward anaphora in the Czech and Croatian language. Both Czech and Croatian are null subject languages, which means that they allow the subject pronoun to be either expressed (overt) or omitted (null). The expression or the omission of the subject pronoun is governed by syntactic and discourse-pragmatic conditions, which means that the speaker must know in which syntactic position the omission of the pronoun is possible, and in which contexts it is appropriate to omit or express the pronoun. In the study we tested three groups of adults: monolingual speakers of Croatian and Czech, and Croatian-Czech simultaneous bilinguals. The task used to test their interpretation of anaphora was a picture selection task. The participants heard a sentence and were shown two pictures. They had to choose a picture which corresponded to the meaning of the sentence. The sentences were complex; the subordinate clause, which contained the null or the overt pronoun, followed the main clause. The main clause contained the subject and an object, expressed by nouns denoting animals. Nouns were matched in gender, number and animacy and were both possible antecedents for the pronoun. There were also some control sentences in the task, without pronouns, which were used as fillers and to check the participants’ concentration level. The results showed that the Croatian monolingual group differed from the Czech monolingual and the bilingual group in the null pronoun condition. The Croatian monolinguals predominantly chose the subject as the antecedent of the pronoun, while the Czech monolinguals and the bilinguals preferred the object. In the overt pronoun condition, all three groups chose the object as the antecedent of the pronoun. In the control condition they all chose the (only) appropriate, subject referent, showing that they understood the task. Overall, the results suggest that the interpretation of null pronouns in Czech, and Croatian may be governed by different discourse-pragmatic conditions.