We investigated a new protein-C (PC) concentrate in a child with a type-II homozygous deficiency, concerning tolerance and safety. By means of various functional and antigen assays the in vivo recovery and the half-life were determined. In order to compare the results we reduced the measured values to the average half-life of 10.0 +/- 0.5 h and to an optimal recovery of 96.6%. Considerable discrepancies observed in the response of functional (clotting) and both the amidolytic and antigen assays are characteristic for type II and anticoagulant treatment. The substituted protein C is activated by the endogenous system. Thus, the efficacy of activation can be determined in deficiency states. The antigen activity of one unit PC concentrate was found to be 120% (or 1.2 U/ml plasma), close to the 100% activity defined for endogenous PC.