A study is reported that investigated American children's use of subjects in early speech and compared this cross-sectional data to longitudinal data on Italian children's production of subjects. Twenty-one American children aged 1.10 to 2.8 years were recorded in mother-child interactions and grouped by mean length of utterance (MLU) produced. Percentages of non-imperative, non-imitative utterances with verbs that also contained subjects were computed. Results suggest that children with an MLU of 2.5 or less understand that English requires subjects and can consistently express that understanding in their speech. Results also indicate that children can infer that it is permissible to omit subjects in certain contexts, but may not always know which contexts support omission. Data from five young speakers of Italian, a language in which null subjects are commonly allowed, at two different stages of acquisition (1.6 to 1.10 years and 2.0 to 2.5 years) show a very different pattern of subject usage. It is concluded that children's use of subjects has been erroneously described in the past, and that none of the current competence accounts of the null subject parameter are supported by these data. Methodological questions about interpretation of inconsistent usage are discussed. (MSE)