The early application of hearing aids in children with severe and profound hearing loss is rather an hard problem that has to be solved, according to the Authors, by taking care of several factors. Usually, as far as these patients concern, two kinds of hearings aids are used. The first one emphasizes all the frequencies in the same way, including low tones that, in the early ages, are very important for improving prosodic pattern, occlusive and liquid phonemas, primary words and sentences. The second type, emphasizing only medium and high frequencies, is useful for discrimination processes. The Authors suggest to applicate the hearing aids in these patients, following a behavior be themselves named "dynamic application". In the first phase the Authors use hearing aids emphasizing also low tones; in the second one they modify the device, according more precise data turning out form audiometric evaluation and speech therapy. The results concerning a research on 27 children with profound hearing loss are debated; the application of hearing aids occurred in early age and the speech therapy followed the same criteria for all patients. The subjects were divided in two groups, homogeneous for age, degree of hearing loss and social environment. For the 12 children of groups A the "dynamic application" was used. For the 15 patients of group B the traditional strategy, using only devices for the amplification of medium and high tones, was applied. The best results concerning voice intonation and learning occlusive phonemas were obtained in group A subjects. The Authors, introducing their results and discussion, compare them with references data. In conclusion, the "dynamic application" is effective because of the better results in speech therapy and also because its ratio permits the application of hearing aids in children with hearing loss of different degrees, especially in the most difficult cases.