Apart from certain changes which are typical for pneumoconiosis, the radiological picture of the lungs of sigma coal miners does frequently show some irregular small opacities of s, t and u types. The role and specificity of these changes in the early diagnosis of pneumoconiosis has not been too well defined by now. A 10-year study (conducted at 2 or 3 year intervals) was carried out among 150 miners from 2 mines characterized by different dust loading. Some irregular changes in the miners' lungs were observed. The control group derived from the same mines comprised 115 miners with no radiological changes found in their lungs. The evolution of radiological changes took place in 55.3% of the miners and was more intensive in the heavily dusted mine. Radiological changes were revealed in 38.3% of the controls. It was indicated that pneumoconiosis results much more frequently (38.6%) from the evolution of the irregular changes rather than directly from the proper radiological picture of the lungs (5.3%). In 44.7% of the subjects the changes of s, t and u type did not undergo any evolution, which may be due to their non-specific characteristics. The evolution of irregular opacities is dominating in the patients with bronchitis and emphysema. No significant correlation between smoking and the progress of irregular opacities was found. The observation of the further exposure to the dusts did not produce any clear results. The progress of the changes of s, t and u type was observed more frequently in those still working under ground, but more cases of pneumoconiosis were found in the miners who stopped working. This fact indicates that the further exposure affects the s, t and u type changes and confirms the observations by other authors concerning the manifestation of pneumoconiosis after the break of exposure. The results of the 10-year study prove that the miners with this sort of changes are exposed to a higher risk of pneumoconiosis, although the answer concerning specificity of irregular changes in the radiological picture has not yet been found.