The clotting time using Russell's viper venum (RVV) was examined in co
mmon carp plasma. The best condition for the assay of RVV time was obt
ained in a 1:30,000 dilution of RVV with Platelin suspension and M/20
CaCl2 solution. Common carp plasma was also subjected to chromogenic s
ubstrate assay for human factor X. The dilution curves of RVV time (RV
VT) and chromogenic substrate assay were made from serial saline dilut
ions of pooled normal plasma. Reductions in coagulation factors had no
marked effects on prolongation of RVV time until reaching a dilution
less than approximately 30%. The activity converted from RVVT showed a
linear relationship between the activity converted from chromogenic s
ubstrate assay within the range from 100 to 40%.