Catalase inhibits TXB₂ production in collagen but not thrombin-stimulated platelets. Platelet TXB₂production in collagen (10 μg/mL)-stimulated platelets added with and without 250 to 1,000 U/mL of catalase and in thrombin (0.1 U/mL)-stimulated platelets incubated with and without 1,000 U/mL of catalase. Data are expressed as the mean ± SEM of five separate experiments (*P < .05; **P < .01).