Geotechnical site characterization is an important first step in all geotechnical engineering problems. It is important to have a model of the subsurface conditions when doing any geotechnical analysis. To create this profile, samples are taken in boreholes which are then used to infer a subsurface profile. This paper discusses a method that uses fuzzy sets to represent the data collected from samples in a borehole. Then, a fuzzy reasoning system is developed to infer the subsurface profile. The resulting fuzzy system creates a new approach to developing subsurface profiles. (C) 1997 Elsevier Science Ltd.