The transport of ions in solution from a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forest floor in western Washington has been studied by the author (McColl 1969, 1972). Using statistical analyses, it was found that the transport process is largely controlled by three environmental factors, namely, the temperature and duration of the dry period before moisture flow, and the total amount of moisture flow during the movement of wetting fronts resulting from natural rainfall. These dynamic relationships have also been described more closely in terms of cause and effect by a mathematical model developed from both field and laboratory data (McColl 1973), and the mechanism of this transport process has been discussed by McColl & Cole (1968). Seasonal relationships between rainfall, temperature and ion characteristics of the forest floor solution have also been reported (McColl 1972). These cited studies go beyond the many previous descriptive accounts of more 'static' characteristics of forest floor types under Douglas-fir (e.g. Cole, Gessel & Dice 1968; Gessel & Balci 1965; Grier & McColl 1971; Youngberg 1966). Many tension-lysimeter studies have been conducted in Douglas-fir forests (Cole & Gessel 1965; Cole, Gessel & Held 1961; Gessel & Cole 1965; Grier & Cole 1971; McColl 1969; Riekerk 1971; Windsor 1969), and in other forest ecosystems also (e.g. McColl 1970; Ponomareva, Roshnova & Sotnikova 1968; Remezov 1958; Shilova 1959; Smirnova & Sukharova 1964), which have contributed to the knowledge of mineral cycling processes. This investigation adds another dimension to these lysimeter studies, by statistically relating the ionic characteristics of soil solutions to the controlling environmental factors measured concurrently in the field, and extends the author's forest floor studies (McColl 1972, 1973) by examining ion transport in the underlying mineral soil as well as in the forest floor alone. The investigation was conducted at the Allen E. Thompson Research Center in western Washington, within the Cedar River Watershed, 35 miles (56 km) south-east of the city of Seattle. This research centre is operated by the College of Forest Resources, University of Washington. A number of related studies have been conducted at this site, including examinations of the cycling of mineral elements in the undisturbed forest (Cole et al. 1968), and the movement of mineral elements and water in the ecosystem following several treatments, including clearcutting of the forest stand (Cole 1966; Gessel & Cole