To determine whether infective larvae of Dracunculus medinensis contain components of a fibrinolytic system, we placed larvae from cyclops on unheated and heated fibrin plates, with and without streptokinase. Cyclops were infected with larvae expelled from a guinea worm; they were allowed to incubate infections for 7, 14, and 21 days, then were killed with 0.02% HCl to release infective larvae. Larvae without streptokinase, and 7- and 14-day-old larvae with streptokinase, produced no hemolysis after 18 hours incubation on plates at 37°C. Marked fibrinolysis with 21-day-old larvae with added streptokinase was noted. This indicates that these larvae contain proactivator. Experiments with larvae expelled by guinea worms produced no fibrinolysis. No fibrinolysis was produced on heated fibrin plates by either sort of larva. We conclude that proactivator in infective larvae may help them penetrate gastrointestinal mucosa and continue their migration in the human host.