The present article provides an overview, of our current knowledge on the topic of discrimination testing. First. the various goals of discrimination testing are outlined in terms of the objective of the investigation: psychophysics (understanding how the human senses work), Sensory Evaluation I (using the human senses as instruments to evaluate food characteristics) and Sensory Evaluation II (investigating the consumer's ability to discriminate between foods). Then, theories are described allowing the selection of the most appropriate protocol based on the aim of the study. These theories include the Thurstonian approach to product measurements, taking into account the central processing of information in the brain. The effect of experimental factors such as memory, sensory 'fatigue', sample retasting and practice are also considered. The consideration of all these variables will allow the selection of the most suitable protocol for investigations involving discrimination testing. (C) 2002 Elsevier Science Ltd. All rights reserved.