The problem of preserving species diversity of different groups of plants and animals in built-up areas is very urgent because of the growing rate of urbanization. Between 1994 and 1996 we studied land molluscs in Lviv, a city with a big centre containing large areas of parks and forest-parks, where before there were forests, and other types of countryside. The landscape is rather uneven, and the very wet climate is favourable for molluscs, resulting in a rich species composition in the area. In Lviv and in adjacent areas, 58 species have been recorded, 42 of them within the city's limits. Analysis of published records shows that over the last century the number of land molluscs species has remained stable, but some qualitative changes have occurred (Sverlova, 1996). Some typically forest species with closely-defined habitat preferences seem to be vanishing gradually as a result of urbanization. In some cases however, urbanization may be favouring an increase in species diversity of land molluscs through the formation of additional and more variable habitats (weed vegetation, greater variation in light regimes and density of stands), and by penetration of species associated with man into natural forest communities. Two particular urban habitat groups are very poor in mollusc species compositions. The first group comprises lawns, and tree and shrub street plantings. These provide few of the conditions needed by land molluscs. The second group comprises parks planted on areas formerly free of forest, frequently on embanked soils. Here molluscs have limited opportunity for migration. Molluscs communities are represented mostly by species associated with man. The species composition of molluscs in the second habitat group is influenced to a great extent by humans through inadvertent introduction of species associated with man. The deliberate introduction of other species from the local fauna may therefore be expedient. It could promote conservation of land mollusc diversity within the city and formation of more stable artificial ecosystems.