Biological hypothesis in obsessive-compulsive disorder is recent and firstly initiated through pharmacological data. The supporting evidences are scant but sufficiently provocating; the review of the literature data on these hypothesis suggests more questions than concluding responses; the introduction of new psychobiological models (like ethologic, cybernetic, cognitive and behavioral models...) and the functional "cutting" (or the transnosologic approach) of the disorder may allow more specific applications for the neurobiological research, and more refined predictions on clinical and experimental observations (responses to psychoactive drugs, biological abnormalities...).