The plasma concentrations of immunoreactive thromboxane B2 and 6-keto-prostaglandin-F1 alpha were determined in coronary venous blood sampled from open-chested, anaesthetised beagle dogs by local vein catheterisation. Thromboxane levels were high immediately following catheterisation (2.08 +/- 0.75 ng X ml-1, mean +/- SEM, n = 6) and fell over 25 min to 0.48 +/- 0.07 ng X ml-1. Initial trauma of the coronary veins (agitation of the catheter) produced a large but variable increase to 5.13 +/- 2.27 ng X ml-1 (0.1 greater than P greater than 0.05) within 2 min, but arterial trauma (repeated momentary occlusions) produced 0.4 +/- 0.03 ng X ml-1, a value not significantly different from control. After 7 min ischaemia an increase to 0.98 +/- 0.26 ng X ml-1 was detected (P less than 0.05). Reperfusion after 15 min ischaemia caused a fall to 0.43 +/- 0.09 ng X ml-1 at 2 min. In contrast, 6-keto-prostaglandin-F1 alpha levels varied little with trauma but increased to 0.64 +/- 0.14 ng X ml-1 (P less than 0.01) within 2 min ischaemia, remaining elevated. On reperfusion, levels fell to 0.27 +/- 0.06 ng X ml-1 (P less than 0.05) at 2 min, progressively increasing to 0.35 +/- 0.05 ng X ml-1 at 30 min. We conclude that intimal trauma of coronary veins induced thromboxane release and that the physical effects of venous sampling may contribute to apparent thromboxane release from ischaemic muscle. Although transient arterial and venous trauma had no significant effect on 6-keto-prostaglandin-F1 alpha, it is still possible that its release during ischaemia may follow prolonged arterial clamping.