The thrombelastograph (TEG) and bleeding time were performed before and 6h after a single oral dose of aspirin 600 mg in a group of eight healthy volunteers and 12 pregnant patients. Measured TEG variables (r, k, r + k times and maximum amplitude) were unaltered after aspirin although there was a significant prolongation of the bleeding time in both groups. Although the TEG appeared not to detect aspirin-induced changes in platelet function, the TEG measures all phases of coagulation and the unaltered TEG after aspirin suggested a functioning coagulation system.