The use of musical instruments, in the clinical practice, for the behavioral assessment of hearing has a limited possibility to control loudness, and does not restrict the test situation to a determined frequency. A new method of testing infants is through the Sonar System. This program can be used for the behavioral hearing assessment of infants, with the possibility of choosing the frequency range and loudness in which the test will be carried out. The Sonar System is different from other behavioral assessment methods once it offers instruments with standardized sounds and is limited to certain frequency ranges; all controlled by the examiner. With this method, one can offer more precise assessments and researches with better methodological control, once the presented sound will not suffer interferences of the examiner. To use the Sonar System--digital band--to follow up the development of hearing in infants, born at term, from one to six months of age. An average of 30 infants was monthly evaluated. For the assessment the following recordings of instruments were presented: clapper, ganzá, coco and drum. These recordings were respectively set at the frequencies of 3000, 1500, 700 and 500 Hz. All infants went through evoked otoacoustic emissions screening. Statistical analysis revealed significant responses in all of the tested frequencies. Results indicated statistically significant differences in all of the tested frequencies for the second trimester, but not for the first one. The use of the Sonar System (digital band) is recommended for the behavioral hearing assessment of this age group. Since this is a new technique to assess behavioral hearing, the use of the Sonar System should be expanded to other populations and in other social contexts in order to allow and facilitate the assessment, diagnosis and intervention of infants and small children.1857-68