Direct or opportunity labour costs often play an important role in farmers' decision making when it comes to the adoption of new agricultural practices. Too often, however, the dissemination of what are believed to be improved practices is unsuccessful because, among other parameters, the availability of labour within households and its cost have not been considered. This is particularly true for practices that aim at reducing soil erosion problems since they generally require a fair amount of work to implement and maintain, and they tend to yield benefits at best in the medium term. In a study area of northern Thailand experiencing socioeconomic changes, it is argued that labour costs are a major constraint for the adoption of conservation practices generally considered for dissemination by many projects. The main reason for that are the potentially high opportunity costs induced by the increasing importance of offfarm employment, and the high direct costs induced by practices that need to be implemented at periods of time when labour already peaks for normal agricultural activities.