Abstract: An apparatus for collecting antigen, including an allergen exemplified by a dust-mite, dispersed in a motile fluid in a given environment that can be inserted in a section of a pipe of a standard vacuum cleaner hose. The apparatus includes a receptacle whose body is formed of nylon, typically with a pore size of from 15 to 60 .mu.m. The receptacle is coated with an antibody that retains the antigen in a contacting relationship. The apparatus is provided with a removable holder, which assists in locating the apparatus in the pipe of the vacuum cleaner. The apparatus can be used directly in an immunoassay for confirming the presence of, or quantifying, the antigen.