Microbial communities on two churches in Schleswig‐Holstein (northern Germany) were characterized using cultural methods as well as light and scanning electron microscopy. Dilution‐plate counts of fungi [106/g dry weight (gdw) stone] and heterotrophic bacteria (105/gdw) were as high as those reported for soils. Counts of algae (106/gdw) were somewhat higher than those for soils. Biomass expressed as phospholipid phosphate concentration (PLP; 115–137 nmol PLP/gdw) was nearly 10 times that of Antarctic sandstone, at least twice that in an architectural red sandstone, and approached that found in soils. Amounts of chlorophyllawere higher than those for the Antarctic sandstone (known to contain algae and cyanobacteria) and were at the lower end of the range reported for soils. The high biomass is supported by photosynthetic carbon input, and hypotheses are presented that describe the role of these epi‐ and endolithic communities in the weathering of their substrata.