Platelet aggregability and coagulative and fibrinolytic systems were analyzed with regard to positive effects and for side effects of 5% ethanolamine oleate (EO) versus 5% sodium morrhuate (SM) used for endoscopic injection sclerotherapy (EIS). Twelve patients each were treated with each sclerosant. There was a temporary activation of coagulative and fibrinolytic systems within 1 h in both groups. Platelet aggregability was significantly suppressed to 78.6 +/- 8.9% of that before EIS in the EO group, but was activated to 110.0 +/- 10.5% in the SM group at 1 h after EIS. The ratio of concentrations of prostacyclin (PGI2) to thromboxane A2 (TXA2) increased in the EO group and decreased in the SM group after EIS. The clinical effect in the SM group after the initial session was weaker than that in the EO group with regard to endoscopic findings at the second session. As change in platelet aggregability after EIS is apparently induced by alterations in the ratio of PGI2/TXA2, there would be related effects concerning the sclerosants.