Platelet aggregation in fII^MZ animals. Platelet aggregation in PRP derived from either fII^WT or fII^MZ animals in response to thromboplastin was determined. Fibrin polymerization was blocked with Gly-Pro-Arg-Pro. There was no qualitative difference between fII^WT and fII^MZ platelet aggregation (A and B, respectively). However, a modest but statistically significant difference was noted in time to shape change (as determined by negative deflection, C) and time to positive deflection (D).