Notions of similarity underlie a wide variety of access methods in hypermedia and information retrieval. This paper describes a research project, in which similarity measures have been extended to include imprecise matching over different dimensions of structured classification schemes (subject, space, time). The semantic similarity of information units forms the basis for the automatic construction of links and is integrated into hypermedia navigation. A semantic hypermedia architecture is outlined, and a prototype museum social history application is described. Illustrative navigation scenarios are presented which make use of a navigation via similarity tool. Three different measures of semantic closeness underpin the similarity tool. The temporal measure takes account of periods as well as time points. The most general measure is based on a traversal of a semantic net, taking into account relationship type and level of specialization. It is based on a notion of closeness rather than absolute distance, and returns a set of semantically close terms. A method of calculating semantic similarity between sets of index terms, based on the maximal closeness values achieved by each term is discussed. (C) 1997 Elsevier Science Ltd.