Numerous data have indicated that water permeability in living systems is greater than it could be explained by simple diffusion. Electron microscope observations have identified special structures presumed to be water channels. The molecular identity of the first water channel was determined in the early 1990s and named Aquaporin 1 (AQP1). It has been now well documented that aquaporins are members of a large family of small (about 28- kDa/ monomer) integral membrane proteins which exist as tetramers, with each subunit containing its own pore. Mammalian AQPs are believed to fold and assemble in the endoplasmic reticulum before being transported to the cell surface. To date 13 AQP’s have been identified in mammals (AQP0-AQP12); however, functional studies have identified a subgroup of AQPs, i.e. AQP 3, 7, 9 and 10, responsible for both water and glycerol transport, named aquaglyceroporins. Further studies have demonstrated that, apart from water and glycerol, AQPs 3,7, 9 also transport ammonia and urea. Additionally, AQPs11 and 12 named superaquaporins, were localized inside the cells, but until now their functions have not been fully elucidated. AQP defects in the human adipose tissue and liver are recognized as a possible cause of obesity. Numerous data indicate that AQPs contribute to carcinogenesis. Data on the effects of physical activity on AQP are scarce; however, it has been recently demonstrated that AQP expression in skeletal muscle and adipose tissue, but also in the brain, respond to physical stress. Thus, it seems possible that in near future AQP studies will provide more knowledge concerning preventive effects of physical exercise in medicine. Furthermore, there is a growing interest in chemicals affecting AQPs, and it could not be excluded that AQP-targeting drugs will be used in medical practice