We report a functional assay of Protein C on whole plasma using a snake venom called Protac-C. This method is simple, avoids absorption-elution techniques. Also this method can be adopted to a microtitre plate system testing of large number of samples. Functional levels by this test correlated well with the antigenic levels (r = .8) measured by ELISA. Protein C functional and antigenic values in 58 healthy volunteers were 82% and 95.5% respectively. The warfarinized samples showed a lower mean.