We have examined the in vitro effects of increasing concentrations of propofol (5-70 micrograms ml-1), ketamine (10(-6)-10(-3) mol litre-1) and thiopentone (10(-5)-8 x 10(-4) mol litre-1) on the release of preformed histamine and de novo synthesized mediators (peptide leukotriene C4 (LTC4) or prostaglandin D2 (PGD2] from human basophils and mast cells isolated from lung parenchyma and skin tissue and from heart fragments. Propofol, ketamine and thiopentone failed to induce the release of histamine and de novo synthesis of LTC4 from basophils. Propofol induced histamine release from lung (mean 8.6 (SEM 1.6)%) and skin mast cells (3.8 (1.5)%), but not from heart mast cells. Ketamine caused release of histamine from lung (6.2 (0.9)%) and skin mast cells (2.5 (1.5)%). Thiopentone caused a small amount of histamine release from lung mast cells (3.1 (1.2)%). Propofol, ketamine and thiopentone did not induce de novo synthesis of PGD2 and LTC4 from lung and skin mast cells. These results demonstrate that general anaesthetics induce only histamine release selectively from human mast cells.