In the past several years many scientists, consultants and growers in northern Idaho and eastern Washington have noticed a decline in the pH of agricultural soils. The purpose of this study was to compile and generate data for the determination of the causes, rate and magnitude of the pH decline in the region. Soil pH records from the past 40 years were collected from the soil testing laboratories at the University of Idaho and Washington State University. An intensive field pH survey was conducted in northern Idaho from 1982–84 and virgin soil samples were acidified under laboratory conditions.