The achievement of labelling was investigated in a longitudinal study of one mother-infant dyad, using video-recordings of their free play in a period between o; 8 and 1 ; 6. Analysis of joint picture-book reading revealed that this activity had very early on the structure of a dialogue. The child's lexical labels might be regarded as more adult-like substitutes for earlier communicative forms that he had utilized in the dialogue. These were smiling, reaching, pointing and babbling vocalizations, all of which were consistently interpreted by the mother as expressing the child's intention of requesting a label or providing one. Participating in a ritualized dialogue, rather than imitation, was found to be the major mechanism through which labelling was achieved. © 1978, Cambridge University Press. All rights reserved.