Aims: To develop a method to screen antifouling agents against marine bacterial adhesion as a sensitive, rapid, quantitative microplate fluorescent test. Methods and Results: Our experimental method is based on a natural biofilm formed by mono-incubation of the marine bacterium Pseudoalteromonas sp. D41 in sterile natural sea water in a 96 wells polystyrene microplate. The 4'6-diamidino-2-phenylindole (DAPI) dye was used to quantify adhered bacteria in each well. Total measured fluorescence in wells was correlated with the amount of bacteria showing a detection limit of one bacterium per 5 µm2 and quantifying 2 x 107 to 2 x 108 bacteria adhered per cm2. The antifouling properties of three commercial surface active agents and chlorine were tested by this method in prevention of adhesion and also in detachment of already adhered bacteria. The marine bacterial adhesion inhibition rate depending on agent concentration showed a sigmoid shape like dose-response curve. Conclusions: This test is well adapted for a rapid and quantitative first screening of antifouling agents directly in seawater in the early steps of marine biofilm formation. Significance and impact of the study: In contrast with usual screenings of antifouling products which detect a bactericidal activity, this test is more appropriate to screen antifouling agents for bacterial adhesion removal or bacterial adhesion inhibition activities. This screening test focuses on antifouling properties of products, especially the first steps of marine biofilm formation.