Regulatory volume decrease (RVD) following hyposmotic stimulation was studied in isolated turbot, Scophthalmus maximus, hepatocytes. Exposed to a reduced osmolality (from 320 to 240 mosm kg(-1)), cells first swelled and then exhibited a RVD. Volume regulation was significantly inhibited in presence of NPPB, 9-AC, acetazolamide, DIDS and barium. Taken together, these results could suggest that RVD operated via separate K+ and Cl- channels and probably Cl-/HCO3(-) exchanger in turbot hepatocytes. The K+/Cl- cotransporter could also be involved as furosemide and DIOA strongly inhibited the process whereas NEM, a K+/Cl- cotransporter activator, added under isosmotic conditions, led to cell shrinkage. RVD in turbot hepatocytes appeared also to depend on proteins p38 MAP kinase and tyrosine kinase but not on proteins ERK 1/2. Arachidonic acid and leukotrienes could also be involved since inhibition of synthesis of both these compounds by quinacrine and NDGA, respectively, inhibited the volume regulation. Likewise, Ca2+ has been proved to be an essential messenger as RVD was prevented in absence of Ca2+. Finally, this work provides bases for novel studies on cell volume regulation in marine teleosteans.