Introduction: Several animal studies have been performed that demonstrates a relationship between the amount of magnesium ion in the plasma and the hearing thresholds following exposure to noise, Mg++ has been considered as an effective factor in  prevention of noise induced hearing loss in animals.The aim of this study was to discover whether Mg for a long period of time have a protective effect on occurrence of Noise Induce Hearing loss.
Method: The subjects were randomly chosen among individuals who were under training in army service for two months. The subjects were treated in a double-blind manner by placebo and magnesium ion. Threshold estimation and blood examination was performed for all subjects before and after treatment. All subjects were exposed to noise during 8 weeks training in the army.
Results: The statistical difference between two groups which was treated with placebo and magnesium ion was significant.
Discussion: This study is compatible with previous in vivo observations and animal studies demonstrating the protective effects of magnesium on noise-induced impairment of inner ear.

Method and Materials: This cross - sectional survey is carried out in pediatric clinic department of audiology faculty of rehabilitation, TMSU, on spring 1998. 102 top grade ranking children with normal hearing threshold

Results:1- The thresholds were not significantly different at any frequency (P>0.05) in test re-test trials.
2- The test minus re-test threshold for individual ears showed clinically reliable and acceptable range 0-10dB SPL for at least
99.74% of the ears at all frequencies.
3- The threshold differences between right & left cars in two test sessions were not significantly different (P>0.05) except for 14KHz.
4- High- frequency threshold in two test sessions showed no significant difference between girls & boys at all frequencies (P>0.05) (except for 16 & 20 KHz in right ear and 10 KHz in left ear).
Conclusion: This test can be used for evaluation of individual high-frequency threshold in all frequency as test re-tests tria1. Moreover, this test may use as a beneficial tool for monitoring different endogenous and exogenous auditory pathologies.
Consideration: it is found that this research is valid only among situation of this project. Any generalization needs further research.

Background and Aim: High frequency audiometry (HFA) provides a valuable tool and optimal index for distinguishing and monitoring many pathologies of the ear. The purpose of this study was to measure the reliability of HFA threshold in children.
Materials and Methods : In this cross-sectional study , 100 normal-hearing children, of 7 to 13 years old, including 50 boys and 50 girls were examined with a Belton 2000 audiometer and Sennheiser HD 250 earphones in Pediatric Clinic  of Audiology Department, Faculty of Rehabilitation of Tehran University of Medical Sciences.
Results: The threshold differences between right and left ears in two test sessions, were not significantly different except for 14 KHz. HFA threshold in two test sessions showed no significant difference in all frequencies between girls and boys but 16 and 20 KHz in right ear and 10 KHz in left ear.
Conclusion : The test-retest thresholds for iudividual ears showed ±0-10 dB SPL for difference at least  in 99.74 % of ears at all frequencies that is clinically reliable and acceptable.

Background and Aim: While most of the people with tinnitus have some degrees of hearing impairment, a small percent of patients admitted to ear, nose and throat clinics or hearing evaluation centers are those who complain of tinnitus despite having normal hearing thresholds. This study was performed to better understanding of the reasons of probable causes of tinnitus and to investigate possible changes in the auditory brainstem function in normal-hearing patients with chronic tinnitus.

Methods: In this comparative cross-sectional, descriptive and analytic study, 52 ears (26 with and 26 without tinnitus) were examined. Components of the auditory brainstem response (ABR) including wave latencies and wave amplitudes were determined in the two groups and analyzed using appropriate statistical methods.

Results: The mean differences between the absolute latencies of waves I, III and V was less than 0.1 ms between the two groups that was not statistically significant. Also, the interpeak latency values of waves I-III, III-V and I-V in both groups had no significant difference. Only, the V/I amplitude ratio in the tinnitus group was significantly higher (p=0.04).

Conclusion: The changes observed in amplitude of waves, especially in the latter ones, can be considered as an indication of plastic changes in neuronal activity and its possible role in generation of tinnitus in normal-hearing patients.