Abstract: An improved device is used for performing solid-phase chemiluminescent immunoassays. The device comprises a container having a fibrous matrix and a porous absorbent material. An improvement in the device is the use of light absorbing material as the absorbent material or as a light barrier between the fibrous matrix and the absorbent material. A second improvement comprises a fibrous matrix of binderless fiber matrix, such as glass fiber. The invention improves the direct measurement of the chemiluminescent signal from a solid surface by reducing background signal. The device is disposable and is suitable for manual use or for use with an apparatus having programmed instructions. The device is designed to be employed in a variety of solid-phase diagnostic assays such as sandwich or competitive binding assays. The device is also designed for use with microparticle capture or ion capture methods of separating the immunochemical reaction products.