A method and apparatus for determining coagulation times in such clinical laboratory procedures as prothrombin times tests, activated partial thromboplastin time tests, fibrinogen determinations, factor assays for specific blood coagulation factors, and the like. A fibrous filament is drawn at a predetermined rate through a small body of liquid to be tested and the interval, from the time a suitable coagulating agent is mixed with the liquid to the time the body of liquid clings to the filament and moves with it, is precisely measured as a direct indication of actual coagulation time. The liquid body is supported upon a non-wettable inclined surface bordered by walls defining a well for receiving the liquid and a pathway for its movement. Particularly effective results are achieved by utilizing a pair of spaced filaments moving at precisely the same rate, the filaments being bridged by a web or mass of clotted liquid when coagulation occurs. A photodetector senses movement of the clot and a timer automatically measures the time between coagulant addition and clot formation. After clot detection occurs, an arm lifts the paired filaments from the well while at the same time directing the advancing filaments through slots to strip coagulum therefrom, then lifts the filaments out of the slots to permit fresh filament sections to move into place, and finally lowers the fresh sections onto a clean inclined surface for another coagulation test. Means are also disclosed for gently agitating the coagulating agent or agents prior to admixture with the test liquid, for insuring proper suspension of the reactants, and for reducing risks of infection and cross contamination during use of the apparatus.