The purpose of the observational system presented here is to record the behavioral interactions between infant and mother, focusing on the sequential and contextual features of the social communication patterns accessible through direct home observation of mothers and their 3- to 4-month-old infants. The present system of continuous data recording allows responses in sequence rather than time to be the units of behavior, thus preserving the actual periodic features of individual behavior and temporal characteristics of interactional exchanges. Recorded are frequency, duration, sequence, inter-response times and simultaneous occurrence of specified maternal and infant behavioral variables. As the infant-mother pair is observed, the behaviors of each continuously qualify as one of a defined set of possible 2- or 3-digit coded behavior patterns, each composed of combinations of basic behavior categories, definitions of which fill one half of the manual. This system uses the Data-Myte or any similar mechanical event recorder, handheld and connected to a cassette recorder worn on the shoulder, giving the observer complete mobility. The observer records (1) the setting, (2) infant arousal state, (3) maternal proximity, (4) maternal behavior and (5) infant behavior. Each session consists of a feeding, a bath and playtime. The manual includes detailed instructions on equipment and general setup. A sample Interview and Rating Scale Form is included for use in writing up developmental and other background data, as well as for recording measurements of subject performance. (BF)