Patients with dysfibrinogenemia demonstrate a low concentration of plasma fibrinogen. However, many cases remain a symptomatic and are incidentally identified on a pre-operative or screening test for pregnancy. Therefore, urgent diagnosis is desirable. To diagnose this abnormality, it is important to demonstrate a discrepancy between test results by the Clauss and immunologic methods. We use a single radial immunodiffusion (SRID) method to measure the fibrinogen level immunologically. We present one dysfibrinogenemia case diagnosed by SRID. The present case was 23 year-old pregnant female. She demonstrated a low plasma level of fibrinogen (91 mg/dl by the Clauss method) on a pre-delivery-screening test in the 39th week of pregnancy. We suspected dysfibrinogenemia, and measured the fibrinogen level immunologically with SRID. Briefly, we dissolved agar in 10% PBS solution and added 1 mg/ml anti-fibrinogen antibody. Then, patient plasma and 50-200 mg/dl of control plasma were placed on the agar overnight. The immunoreactive fibrinogen level in this patient was 400 mg/dl. Therefore, we diagnosed her as dysfibrinogenemia. She did not have a bleeding episode during the normal vaginal delivery even through fibrinogen was not transfused. The SRID method is readily available, and requires only an anti-fibrinogen antibody and agar, both of which are usually stocked by a general laboratory. The practical method and application described in this report provide instructive information for hospital laboratories.