The purpose of this study was to investigate blood platelet function during exposure to the hydrophobic organic solvents toluene, p-xylene and n-hexane. Human blood platelets were exposed for 30 min at 37°C to a saturated atmosphere of p-xylene, toluene or n-hexane. All three solvents, and the aromatics in particular, induced a decrease in the number of single platelets (61-88%) together with an increase in the extracellular levels of ATP plus ADP (45-65% of total) and serotonin (67-100% of total). Passive leakage of [(14)C] adenine-labelled nucleotides from the metabolic pool, due to platelet lysis, was minor or delayed. Electron microscopy of platelets exposed to p-xylene revealed aggregation. The platelets were spherical without pseudopods. Our results indicate that the hydrophobic solvents n-hexane, p-xylene and toluene induce platelet aggregation and dense granule secretion.