Summary: Stuttering is a serious health and social problem, which is reflected in socialising processes and job opportunities. It is a generalised discoordinative disorder of muscle groups, that take part in motor realisation of speech. The prevalence in population differs according to various authors from 1 % to 3%, of which men prevail. The opinions on etiology and therapy differ a lot, causes can be either somatic, functional or psychogenic. A positive effect of delayed auditory feedback (DAF) on speech in stutterers has been known since 1951 (so called Lee effect, named after its discoverer). There is supposed to be a disharmony between proprioceptive and auditory feedback, which is corrected by delayed auditory feedback. The optimal interval of DAF should be 55 ms. Considering that the former technologies were not able to study shorter intervals, we focused our study on intervals shorter than 55 ms and we tried to find an optimal interval of DAF. Most of previous research studied the influence of DAF on reading. Considering that severity of fluency disorder is usually smaller when reading than in spontaneous speech, we decided to study the influence of DAF using description of standard pictures. Our group of patients consisted of 41 stutterers (35 women and 6 men), aged from 8 to 35, the mean age was 15 years. We found out that 16 patients (39%) improved in speech fluency under the influence of DAF with delay speed 55 ms, which is in good accord with previous studies. However, in 8 patients (19%) speech fluency was improved using delay speed 40 ms especially in patients aged up to 15 years.We proved then that speech fluency in stutterers can be improved by using intervals shorter than 55 ms. In 13 patients (32%) we observed positive effect from delay 110 ms, mostly in patients with severe form of stuttering. Four patients (10%) did not improve at all. Normal fluency under the influence of DAF was reached by 10 patients (24%) who had mild or medium stuttering. We also observed self evaluation of patients which is not always in accordance with objective evaluation. From the group of 23 patients the accordance was reached in 7 patients, another delay interval was subjectively more pleasant in 10 patients, for 5 patients DAF was not pleasant at all and one patient was not able to assess subjectively improving or worsening. We can use the positive effect of DAF in treatment. At present there exist not only large- sized devices using DAF but also miniature devices that look like behind the ear hearing aids.We usually use table devices as an aid during speech therapy

        Key words: stuttering, delayed auditory feedback, DAF, Lee-effect.