The results of bryological studies that were conducted on the territory of Katowice are presented. Katowice is the largest town in the main Polish industrial region (Silesia Province). The goal of the paper is to evaluate the impact of human pressure and the spatial structure of a town on the distribution of moss species. A great deal of habitat diversity is reflected in the quite high species richness. The moss flora includes 192 species, from which 14 are considered endangered in the national red list, seven are regionally endangered in the Silesia Province (four of those included in the former list and another three), and 48 taxa are under legal protection by the Polish government (36 not included in either of the former lists). In heavily urbanized areas of the city the number of species usually does not exceed 20 in one square kilometer. In squares that were more differentiated in regard to habitat conditions and in those with a greater forest cover, species richness amounted to almost 60. Some ecological aspects are discussed, e.g. the spatial polarization of calciphilous and acidophilous bryoflora.