As well as physiological states, pathological states and therapeutical problems may be a gushing spring for biological theory-and conversely

New class of therapies, including bipolar therapies (BPT) and "paradoxical" unipolar therapies (PUT) were firstly proposed in relation to a clinical i nsight and to some results of biological investigations, then they gave ris e to mathematical modeling which brought a justification of these therapies , at least from a theoretical point of view. After recalling the mathematic al model for the regulation of agonistic antagonistic couples, and reportin g the fundamental types of control simulation by means of it, we point out the validity of therapeutical applications inferred from this model. These therapy modalities, including BPT and PUT, now concern the following diseas es: astrocytomas, epilepsia and trials on multiple sclerosis. Even if such attempts are in their early stage, noticeably for the last case where biolo gical changes have mainly been studied, it seems that a large span of treat ments is open to BPT and PUT. Improvement of these techniques in the future depends, in our opinion, on a parallel working on the dynamics of the math ematical model and the dynamics, perceived by clinical insight and confirme d by biological investigations, of the body reactions to such strategies. J ustification of BPT and PUT was given, by resorting to the notion of "patho logical homeostasis" which, too often, intervenes in order to nullify the e ffects of unilateral (not paradoxical) therapies. This research has elicite d some therapies which use two agents with antagonistic effects or only an agent with effects similar to the agent already in excess in the body - in both cases at nearly physiological doses.