An immunochromatographic assay was developed to detect fluoroquinolone antibiotic ofloxacin based on the competitive binding of ofloxacin and the membrane-immobilized ofloxacin-protein conjugate to colloidal gold-labeled antibodies in the course of the labeled antibodies, and to test sample flow through the membrane. The specific feature of labeling by colloidal gold is that native antiserum is used instead of purified immunoglobulins or specific antibodies. This makes the synthetic procedure easier, with no sacrifice in the detection limit. The proposed test makes it possible to detect down to 30 ng mL(-1) of ofloxacin, which corresponds to the demands of food safety assessment. The assay time is 10 min. The assay provides reliable information on the ofloxacin content in milk without the sample preparation and in chicken and pork meat with the minimum sample preparation (the separation of the insoluble fraction of the homogenate by centrifugation). The high degree of detection of ofloxacin in foodstuffs by the proposed assay (70-112%) was shown by a comparison with the data obtained with the use of a commercial immunoenzymatic kit.