A method is described for electroblotting of proteins, separated by gradient polyacrylamide gel electrophoresis, onto an agarose gel matrix containing specific antibodies. Three proteins of different molecular weight, including human albumin, isolated and in plasma, human plasma transferrin and C3 complement were tested. Immunoblotting on agarose, compared with nitrocellulose, was quantitative and highly sensitive, with small amounts of protein (i.e., 100 pg) being detected. Moreover, albumin aggregates (i.e., dimer, trimer and tetramer) were blotted quantitatively in addition to the monomer, and their percentages were calculated. This method is sensitive, quantitative, reproducible, and includes fewer manipulations; furthermore, it is less expensive and does not require the use of toxic or carcinogenic agents.