A sound theoretical basis supported by scientifically measured physiological parameters is needed to gain medical support for animal-assisted therapy. Six neurochemicals associated with a decrease in blood pressure were measured in humans (n=18) and dogs (n=18) before and after positive interaction. Results (P<.05) indicated that in both species the neurochemicals involved with attention-seeking or attentionis egens behavior have increased. This information can be used as a rationale for animal-assisted therapy.