Platelet aggregation rate (PAR), plasma concentration of TXB2 and 6-Keto-PGF1 alpha were measured in 26 patients with shock (hypovolumic shock 10 and septic shock 16) and 10 controls. PAR, plasma TXB2 and 6-Keto-PGF1 alpha were increased during shock, with TXB2 increased more significantly than 6-Keto-PGF1 alpha, accordingly the TXB2/6-Keto-PGF1 alpha ratio were raised during shock, especially in the septic cases. PAR, plasma TXB2 and 6-Keto-PGF1 alpha will decrease while shock become subsiding, and elevate while shock become irreversible. As a rule, the change of PAR is parallel with the concentration of plasma TXB2. The speed of platelet aggregation and plasma TXB2 concentration were higher in eleven mortal cases.