A variety of methods for preparing human immunoglobulin G (IgG) specific immunoadsorbents have been compared. All preparations have been based on cellulose and its derivatives, and the suitability of this polysaccharide as a carrier has been investigated. The relative efficiencies of different protein immobilisation procedures have been assessed with particular reference to the success and practicalities of the carrier activation procedure and the capacity to couple antibody protein. Once immobilised the activities of the antibodies were measured in terms of the capacity for antigen using radioimmunoassay procedures and comparisons were made with free antibody. A number of different eluting agents were used to recover antigen, and the relative effectiveness of these agents was determined. The most efficient immobilisation procedures were those involving coupling of the antibody to diazotised N-(3-aminobenzyloxymethyl) cellulose, glutaraldehyde activated aminoalkyl cellulose or bromoacetamidoalkyl cellulose. These methods were used to make immunoadsorbents for use on a preparative scale and in solid-phase radioimmunoassay. Immunoadsorbents were used as the basis of sensitive and specific radioimmunoassays for IgG, IgD, insulin and human placental lactogen. Immunoadsorbents specific for human IgG were used in various purification protocols involving different combinations of batch and column immunoadsorption, washing and elution. The findings were then applied to the purification of IgD from both myeloma and normal sera. The IgD was characterised both physically and immunochemically.