A self-contained reagent package device for an assay comprises a support member and a plurality of wells in the support member. All of the wells are capable of retaining liquids therein. At least one of the wells has an aperture at its bottom end for the passage of liquids therethrough. The one well includes a carrier to which a reagent is bound and further includes a porous filter positioned between the carrier and the aperture which is capable of retaining liquids used in the assay under normal atmospheric pressure conditions. The filter permits the passage of those liquids, including unbound and soluble substances, at increased pressure within the one well. Further, the filter is capable of retaining the carrier and substances bound thereto. At least one of the wells includes a predetermined amount of reagent therein. Another of the wells is empty so that the specimen to be assayed may be deposited therein. A removable protective cover is sealed over the open ends of the wells to maintain the incorporated reagents in stable form prior to use. A method for the performance of an assay using the above-described device is another aspect of the present invention.