Abstract: The flow injection system was based on the use of Folin - Ciocalteu reagent, with 1,4-dithio-DL-threitol to accelerate the formation of the colored complex, which was detected at 700 nm. The calibration graph for bovine serum albumin was rectilinear between 0.01 and 0.1 mg mL-1. The detection limit was 5 µg mL-1 and up to 0.5 mg mL-1 could be determined. The injection frequency was 20 h-1. Results obtained by the flow injection method and by the manual Lowry procedure correlated well. Egg lysozyme, alkaline phosphatase and β-lactoglobulin were also determined.