A new in vitro model is proposed for studying the spatiotemporal distributions of activated clotting factors, in which clotting is activated in a thin layer of non-stirred plasma supplemented with a fluorogenic substrate and is monitored by fluorescence from its cleavage product. Analysis of the spatiotemporal dynamics of factor XIa and kallikrein in glass-activated human plasma provides evidence that both contact factors remain restricted to the glass surface and possibly a narrow boundary zone (<0.1 mm). The kinetics of factor XIa and kallikrein studied by a new method (in non-stirred plasma) coincided with those studied fluorimetrically with full stirring: their concentrations rapidly rose for the first few minutes after activation and then slowly declined. Factor XI and prekallikrein activation is likely to be restricted by the limited number of sites available for binding to the surface. The maximum concentration of the active factors was estimated at 2 x 10(8) molecules per mm(2) at the glass surface (irrespective of stirring). At the plastic surface, this value was 15--30 times lower.