Information concerning the audiometric status, noise exposure, and exposure to chemicals was gathered from 3860 Polish workers from different industries, including a coal mine, an electric power station, a dockyard, a glass bottle factory and a lacquer and paint factory. An inclusion criterion for this study was an exposure to noise of at least 3 years. Subjects with a history of middle ear disease, conductive hearing loss or skull trauma, and subjects with a family history of hearing loss were excluded. Among the Polish workers only a minority had been exposed to noise during 20 years or more, which is in contrast with the situation among the Swedish workers. Therefore it was decided to evaluate the HTLs at 4 and 6 kHz instead of 3 kHz since 4 and 6 kHz are most easily affected by NIHL. In former genetic studies on these noise-exposed workers, the 10% most resistant and sensitive subjects were selected using a Z-score based on the ISO 1999 (ISO 1999 – International Organization for Standardization, 1990) (Sliwinska-Kowalska et al., 2006), leading to a selection of 347 sensitive and 338 resistant subjects (Konings et al., 2007). Age and noise exposure level in this initial selection were not equally distributed between resistant and sensitive workers. This resulted in significant effects of the interaction between age and noise exposure level and quadratic effects of age and noise exposure level. The statistical analysis that was applied corrected for these differences and interactions in age and noise exposure between resistant and sensitive workers (Konings et al., 2007). Although this approach was valid, it led to a complex statistical model of which the results were difficult to interpret. That is why we opted to perform a stricter and matched selection of resistant and sensitive subjects. Additional exclusion criteria were applied, such as exclusion of female subjects, exclusion of subjects with a history of extended treatment with aminoglycosides, the duration of exposure to noise had to exceed [(age * 0.666) – 20 years] and finally, no subjects were included that had been exposed to noise in a previous workplace longer than 15 years. Next, the remaining population of 3390 Polish workers was divided into 9 categories (three years of exposure ranges, below 15, 15 to 25 and above 25 years, and three occupational noise exposure categories, ≤85 dBA, 86–91 dBA and ≥92 dBA, all leq, 8h, 5 days a week). Subsequently, the mean left ear HTL at 4 and 6 kHz was calculated for each subject. From each category, the 20% most resistant and the 20% most sensitive persons were selected. At this level, additional exclusion criteria were applied to the sensitive subjects only. These could not have a history of meningitis, acoustic trauma or aminoglycoside treatment or an asymmetry between the right and left ear of more than or equalling 40 dB. Finally, they should not have been exposed to noise in a previous workplace for more than 5 years. For genetic analysis, we were limited to the subjects from whom DNA was collected, which are the subjects who had been selected as resistant or sensitive subjects using the previous selection procedure based on the ISO 1999. For each resistant subject, a sensitive subject for factory and age (+/− 10 years), was matched. This selection procedure resulted in 119 pairs of samples, 119 resistant and 119 sensitive subjects.