[Chronotoxicology, a relatively unknown approach in toxicology].

Biorhythmicity of living organisms is well-known for many decades by numerous studies in cell biology, in physiology and more recently in pharmacology. Reality of temporal changes in structures and functions of biological systems is clear whatever their complexity level. Such temporal variations can explain that the same xenobiotics, whatever its origin (pathogenous, medicamentous or toxic) does not induce the same efficacity or side effects in a living organisms, if it is given at different hours in the day or at different seasons in the year. This review considers the classical and recent data of the temporal dimension of the toxicology, so called chronotoxicology, describing as well experimental aspects as clinical ones showing the influence of time administration of drugs largely used in clinic with a poor unfair therapeutic index on their efficacity, tolerance and toxicity. Toxicological studies using lethal or sublethal doses with specific organ targets as liver, ear, digestive tractus or kidney will be described. Conclusions of this review evidence the necessity to precise for such chronotoxicological experiments the time of the day and the month of the year where they are performed.