A longitudinal study of language development is being conducted in which ten recordings of spontaneous speech are being made of l28 children at 3-month intervals. Children were stratified with respect to age, sex, birth month, social and educational family background and family occupations. A matrix was constructed for two groups of children, with entry ages of 15 months and 39 months. Recordings are made with a radio-microphone worn by the child. The radio receiver and the tape recorder are placed in the home and programmed to switch on for periods of 90 seconds at intervals of about 22 1/2 minutes between 9A.M. and 6P.M. The recording is later played to the mother to determine as much of the context and circumstances of the speech as possible. In the printed transcripts (not included here), the child's speech is in the left hand column, the speech of other participants in the center and contextual information on the right. Interpretations of utterances and descriptions of intonation are included where applicable. So far, the first recordings of each child have been transcribed and prepared for publication, totaling about 2500 pages. (CHK)