The influence of catamine AB, sulfonol NP-3, sodium alkylsulfate homologues (C10-C16) and of syntanol DT-7 on the reaction of fibrin formation under the action of the partially purified coagulase was studied. Catamine and sulfonol inhibited the velocity of the reaction in the the concentrations over 0.002 and 0.01%, respectively. A reduction of the rate of reaction with catamine occurred chiefly as a result of the enzyme inactivation, whereas sulfonal influenced the intermediate products of the reaction. Inhibition of the rate of the reaction with the sodium alkylsulfate homologues was enhanced with the increase of the alkyl radical length and was the greatest for the tetradecyl sulfate sodium. Syntanol failed to influence the enzyme activity, but increased its amount in the staphylococcus culture on the medium with subbacteriostatic concentrations of sulfactants. Catamine, sulfonol and, to a lesser extent, syntanol retarded the coagulation process of human citrate plasma with pathogenic staphylococcus.