Clinical observations and novels in the 19th century recognized that memory of some events can be retrieved only under the influence of the same drug condition that was present during the event. This dissociative effect of drugs probably reflects the same drug effects that were later called the discriminative stimulus effects of drugs. The Society for Stimulus Properties of Drugs (SSPD) was founded in 1978 as a forum for communications and periodic meetings on this drug effect. During its early years many of its members were psychologists, but subsequent to that time the most frequent research application has been for the pharmacological purpose of identifying new drugs that have the same discriminative stimulus attributes as a prototype training drug. The majority of members have been in the United States, but several major international meetings have been in Europe. The methods used by the society's members involve both neuropharmacological and psychological processes, allowing them to make unique contributions to the study of both mind and brain.