A study was conducted of the language development of a hearing child whose mother was deaf and communicated only in sign and whose father was hearing and communicated in both sign and oral language. Results showed similarities in development between the two modalities as well as similarity between development in two separate modalities and two oral languages. Manual and oral "babbling" occurred in early stages, and one-word utterances preceded combinations of words. In later development, lexical code-switching began, in which the child chose her code based on the communicative needs of her addressee. Interference surfaced when syntactic constructions permitted in only one modality occurred in the other. Two separate, complementary lexicons developed, with little overlap of lexical items. However, at the onset of code-switching, the child began to distinguish between the two lexicons. The occurrence of a particular lexical item was greatly influenced by the contextual conditions in which it was learned. Thus, the rate and sequence in which semantic relations emerged in signing paralleled that of oral language, and learning in two modalities with approximately equal exposure to both codes did not affect semantic development. (PJM)