Activation of rat basophilic leukaemia cells (RBL-2H3) leads to the secretion of allergic and inflammatory mediators. These cells can be permeabilized, yet still retain their ability to secrete in response to antigen. Secretion can also be induced in permeabilized cells by the addition of the ATP analogue, ATP gamma S [adenosine-5'-O-(3-thiotriphosphate)], which is relatively resistant to phosphatase activity. ATP gamma S-induced secretion (35-50% of total amine) is temperature and concentration-dependent. Calcium enhances secretion, but unlike antigen-induced secretion, it does occur in the absence of calcium and without the requirement for inositol phospholipid hydrolysis. Other ATP analogues induced secretion in the rank order AMP-PNP > or = ATP gamma S >>> AMP-PCP > ATP alpha S = ATP [AMP-PNP, adenylyl-imidodiphosphate; AMP-PCP, adenylyl (beta,gamma-methylene)-diphosphonate; ATP alpha S, adenosine-5'-O-(1-thiotriphosphate)]. At equimolar concentrations, ATP inhibits ATP gamma S-induced secretion by 50%, but prolonged incubation in the presence of ATP gamma S surmounts the ATP inhibition. ADP is nearly as effective an inhibitor, but GTP and ITP are ineffective. It is likely that secretion occurs through attachment at an ATP-binding site, effectively blocking the action of a phosphatase, active later in the normal secretory pathway.