Our experience in the use of Ellis' and Stransky's turbidimetric technique for the determination of plasma fibrinogen is presented. We standardized the test using a plasma pool whose fibrinogen content was determined by a weighed clot technique. The turbidimetric-fibrinogen test is accurate, sensitive, specific, reproducible, convenient, and inexpensive. Correlations between the turbidimetric method and the weighed clot reference method was shown. The assay is sensitive to as little as 25 mg/dl plasma fibrinogen, and the results are not affected by samples with a high content of lipids, bilirubin, fibrin split products, lymphangiogram dye, or therapeutic levels of heparin. Day-to-day replicate determinations on a plasma pool yielded a coefficient of variation of 3.4 percent. Results from as many as 10 plasma samples can be obtained in 30 minutes (10-minutes working time). Reagent cost is less than one cent per test.