The inflammation is characterized by a multifrequency time structure described both in the edematous reaction and in the migration of neutrophilic polymorphonuclear (PMN) in the inflammatory site. The circadian rhythm of PMN migration appears to be similar when the migration was induced by BCG, LPS or carrageenan. The corticosteroids play an important role in the mechanisms in the circadian rhythm of PMN, but recent data in intact and castrated mice indicated that testosterone is also involved in these mechanisms. In arthritic patients, the signs and symptoms of the diseases varied as a function of time of day and of the type of arthritic diseases. Human data with indomethacin, ketoprofen and piroxicam indicated that it is possible to find an optimal time of day for the administration of these non-steroidal anti-inflammatory agents (NSAID). Clinicians can use these chronopharmacological data to maximize the analgesic effect and to minimize the side effects of the NSAID. The research on biological rhythms in inflammation and in the effects of NSAID lead to a better understanding of the mechanisms of inflammation and to the rational use of the drugs in arthritic patients.