The present study was conducted in order to determine whether or not HR could be conditioned in 3 month old infants. The conditionability of HR as an autonomic response was viewed in terms of Brackbill and Fitzgerald's (1969) hypothesis regarding differential conditioning results as a function of measuring an autonomic rather than a somatic response. The relative scarcity of conditioning studies measuring autonomic responses prompted a study by Clifton (1970, unpublished data) which yielded inconclusive results. The present study was designed as a replication of the Clifton study with several modifications