Changes in coagulation parameters were studied in dogs naturally infected with Babesia canis canis (n = 30), and haemostasis was evaluated and compared to values obtained from healthy dogs (n = 29). To date, there have not been any studies examining the dynamics of thrombin-antithrombin complex formation in cases of canine babesiosis. Coagulation parameters evaluated before (day 0) and on days 1, 2, and 3 after treatment with imidocarb (6 mg/kg inj. s.c.) included the determination of platelet counts, the formation of thrombin-antithrombin complexes (TAT), prothrombin time (PT), activated partial thromboplastin time (APTT) and antithrombin III (AT III) activity. TAT complexes were significantly elevated in animals with babesiosis on days 0 and 2 (mean 49.7 and 87.7 microg/L vs. control, 7.2 microg/L). AT III activity was significantly decreased at all time-points examined. There were no differences in PT. On days 2 and 3 the APTT was significantly shortened in the infected dogs when compared to control animals (means of 21.3 and 19.2 s vs. control, 30.0 s). Our analysis demonstrated that infected dogs had significant thrombocytopenia during the course of the study (mean day 0 - 29 x 10(9) /L, day 1 - 48 x 10(9) /L, day 2 - 47 x 10(9) /L and day 3 - 87 x 10(9) /L, vs. control -259 x 10(9) /L). These data suggest that babesiosis in dogs compromise primary and secondary haemostasis and that induction of disseminated intravascular coagulation (DIC) occurs in canine babesiosis.