The physicochemical properties of soils, which determine how readily the soils wet, were shown to vary significantly in mountain soils collected at six sites in southern British Columbia, even within individual profiles. The results of water drop penetration time tests were used to classify samples using a very simple scheme which is based upon our current understanding of the possible physicochemical interactions between solid surfaces, water, and soil air. In all cases where the samples were collected at sites in the subalpine-alpine ecotone, a layer which either wets reluctantly or is water repellent exists at or near the surface of the profile. These layers occur only where there is evidence for accumulation of organic matter, and are usually no more than a few centimetres thick. At the one site which was below the alpine-subalpine ecotone, the soils wet readily throughout the profile. These results suggest that the type of organic matter which accumulates in soils of the alpine-subalpine ecotone of southern British Columbia either limits the affinity of soils for water or renders the soil water repellent. The relation between infiltration rate and ponding depth was explored experimentally for a set of soil samples from a site in which a repellent layer was developed to depths greater than thirty centimetres. It was found that the infiltration rate, which was less than 2.0 millimetres per day for all samples, was insensitive to changes in the ponding depth to a maximum applied depth of 400 millimetres, and that it remained approximately constant over time. These results suggest that water was transported primarily as a vapour rather than as a liquid. Given that water repellent soils are not uncommon in the alpine-subalpine ecotone of southern British Columbia, and that ponding depths on hillslopes would be several orders of magnitude less than those applied experimentally, it is inferred that transfer of water as a vapour within may be an important mechanism in such environments. In their interpretation of variable solute sources and hydrological pathways in a small subalpine basin in British Columbia, GALLIE & SLAYMAKER (1984) suggested that water repellency could account, in part, for the observed tendency of water to bypass the soil matrix. They noted that water repellency seemed to be preferentially associated with three of the six soil-vegetation complexes found in their field area. In explaining the relatively low solute yields from these same soils, GALLIE & SLAYMAKER (1985) inferred the importance of hydrophobicity in years when segregated soil ice did not form. Reasonable though these assumptions were, they were based on inference from scattered observations and BARRETT's Masters thesis (1981). No systematic analysis of the phenomenon of water repellency was undertaken. Water repellency appears to be associated with accumulation of certain types of organic compounds on mineral grains. BOZER, BRANDT & HEMWALL (1969) suggested that the molecules involved are probably amphophilic; that is, they have a polar end which is attracted to mineral surfaces, and a nonpolar end which is directed outwards to form a hydrophobic surface (fig.1). It has been documented that forest fires and slash burning may result in transformation, volatilization, and distribution of organic compounds to produce a repellent layer, which may revert to a non-repellent condition over a number of years ( DEBANO, MANN & HAMILTON 1970, SAVAGE, OSBORNE, LETEY & HEATON 1972, REEDER & JURGENSON 1979, and GIOVANNINI & LUCCHESI 1983). Fungi and algae have been implicated in the production of water repellent soil ( BOND & HARRIS 1964, SAVAGE, MARTIN & LETEY 1969, and MILLER & WILKINSON 1977), as have a variety of plant species, especially those native to semiarid environments. The vegetation implicated includes: Chaparral in California ( KRAMMES & DEBANO 1965), Juniper in Utah ( SCHOLL 1971) and Mallet trees in Australia ( MCGHIE & POSNER 1980). As far as the authors are aware, there has been no previous documentation of water repellency as characteristic of soils in the alpine-subalpine ecotone of southern British Columbia. This paper begins with a discussion of the conceptual basis for characterization of the physicochemical properties of soils in general, and of water repellent soils in particular. The results of field studies of water repellent mountain soils at the site studied previously by GALLIE & SLAYMAKER (1984, 1985) and at other sites in southern British Columbia are presented. The paper closes with a summary of the results and conclusions. A subsequent paper will explore the implications of this phenomenon for overland flow and runoff generation (BARRETT & SLAYMAKER, in preparation).