Three trials were carried out to study the effect of garlic on thrombus formation and patency in the mouse pial microcirculation in response to hyperthermia. Two different hyperthermic exposures, at 43 degrees C for 60 min and at 44 degrees C for 45 min, were applied to the brain surface of anaesthetized mice by heated artificial cerebrospinal fluid (ACSF). Garlic solutions were prepared 24 h prior to their injection, i.p., from a finely-ground powder in saline (pH 7.3) to deliver doses of 25, 50 and 75 mg/kg. Control groups of the three trials were injected with saline, pH 7.3. Garlic and vehicle solution injections were made 60 min prior to the intended hyperthermic exposure. Microvascular responses were monitored and were recorded by intravital videomicroscopy. With core body temperature kept at 37 degrees C and at the elevated ACSF temperatures, the first observed intravascular response was in the form of either passing emboli or as visible thrombosis in either arterioles or venules. Further thromboembolic events continued and throughout such exposures higher arteriolar patency was evident in the garlic-treated mice. Collectively, garlic significantly delayed the appearance of the first observable thrombo/embolic response. Data of this study evidenced that garlic delayed hyperthermia-induced platelet aggregation, in vivo. Such results could prove beneficial to those adversely affected by antithrombotic drugs, like aspirin.