Baby's crying plays important role in mother - infant interaction. Its functions change according to bady's age and situation. The crying is informative and has different senses. It shows baby's need in communication. It shows also infant's ability to make a connection by way of expressive manifestations, which is necessary for its phisiological and psychic development. The crying represents selective reaction to abult's speech and can be considered to be pre-speech activity, possessing language character by the age of two months. Mother - infant interaction is adequate when mother understands subjective meaning of crying and its objective sense.