Development and use of a rating scale to code videotaped mother-child interactions involving 1-year-olds with Down's syndrome are described. It is explained that the ratings were developed to describe individual differences in directiveness and sensitivity in mothers and social and cognitive maturity in the children, with a measure of mutuality or harmony shown by the mother-child dyad. Ten child qualities rated on 5-point scales are described and examples are given: level of play maturity, social initiative, social responsivity, degree of interest in toys/free play situation, object activity initiative, expressed positive affect, expressed negative affect, locomotion, animation, and child appeal. Six mother qualities using multipoint scales are also described: directiveness/control, elaborativeness, sensitivity, stimulation value, mood, and mother appeal. Forms of mutuality as measured in the dyadic rating are described. (CL)