A particularly efficient design for a nonbibulous lateral flow one step assay for an analyte in a biological sample is disclosed. In the improved device of the invention, three zones which are in nonbibulous lateral flow contact are employed: a sample receiving zone, a labeling zone, and a capture zone. The sample containing analyte is carried through the labeling zone and interacts with an assay label comprising visible moieties, preferably particles, which are coupled to specific binding reagent for analyte or to a competitor with analyte for a capture reagent. The flow continues into the capture zone where the visible moieties to which analyte or competitor are coupled are captured. Excess fluid is absorbed into an absorbent zone in contact with the capture zone. A positive result is obtained by visualizing the visible moieties in the capture zone. An additional improvement comprises obtaining the nonbibulous lateral flow by converting a bibulous support to a nonbibulous support through coating with a blocking agent, such a methylated BSA. Control label comprising visible moieties (preferably, visually distinguishable from those of the assay label) may also be included in the labeling zone and captured in a separate control portion of the capture zone to verify that the flow of liquid is as expected.