To assess the discrepancies noted in fibrinogen measurement by the DuPont aca® and Dade® methods, nine patients receiving streptokinase (SK) by either the intracoronary (IC) (240,000 IU/60 minutes) (two patients) or intravenous (IV) (1,500,000 IU/45 minutes) routes (seven patients) for acute myocardial infarctions were studied over 48-72 hours. All nine patients showed a rapid and profound fall in fibrinogen to unrecordable levels (30 mg/dL) by the Dade method. Three patients showed a similar response to unrecordable levels (<50 mg/dL) with the DuPont aca method. Six others had less of a decrease with the DuPont aca method compared with the Dade method. One patient showed a gradual fall by the DuPont aca method to reach 60% of the preinfusion level at 30 hours, whereas the minimal value by the Dade method, 81% of the preinfusion level, was reached within 12 hours. There was no difference in fibrinogen levels by the Dade method after absorption of heparin-like activity with triethylamino ethyl (TEAE) cellulose. Fibrinogen degradation products (FDPs) were elevated in all patients post-SK infusion. These studies show that fibrinogen estimation by DuPont aca and Dade methods may yield discrepant results in approximately 66% of patients treated with SK. This may have some clinical relevance to clinicians who rely on the DuPont aca fibrinogen estimation to monitor effectiveness of SK therapy.