Fic; 1. Platelet counts in w. hole blood anticoagulated with both hirudin and soybean trypsin inhibitor and incubated at 37 C. The difcrcnce between the number of platelets in samples fixed with formalin (-----) and the number of platelets in control samples mixed with EDTA buffcr (-) rcflccts the formation of platelet aggregates. Mechanical disturbancc of the blood at the time of rampling was standardized by invcrting thc tube slowly four times, to mix red cells evenly\vith plasma. Bars=+ SEM; ri= 3. concentrations were less than 0.04 pg/ml in all samples. P-Thromboglobulin concentrations were equal in the tw'o series and always less than 0.3 pg/ml. The experiments on whole blood were repeated using only one of the anticoagulants at the time. Identical results wcre obtained in those two series, equal to the findings when hirudin and soybean trypsin inhibitor (SBTI) were used together. In Fig 3 platelet aggregate formation in citrated whole blood (11 mM) is compared with blood containing SBTI only and with blood containing a mixture of the two. Citrated blood

0 15 30 a5 60 incubation time (min 1