A multianalyte enzyme-linked immunosorbent assay (ELISA) has been developed for the simultaneous detection of anabolic androgenic steroids (AAS) in human serum. The multiplexed method was developed according to a planar strategy in which the analytes are identified by their location in the microtiter plate. In the immunochemical procedure established here, human serum samples are mixed with a cocktail of antibodies and added to the distinct sections of a microplate biofunctionalized with different haptenized biomolecules. The cocktail of antibodies consists of a mixture of polyclonal antibodies raised against stanozolol (ST), boldenone (B), and tetrahydrogestrinone (THG). The whole immunochemical analytical procedure takes around 2 h including sample preparation, and many samples can be processed simultaneously to screen for the presence of the three AAS in a single run. Using this ELISA, ST, B, and THG can be detected and quantified individually. When used as a screening method, due to the cross-reactivity profiles of the immunoreagents used, the presence of up to 11 AAS can be detected simultaneously. The detectabilities achieved by this method in human serum are below the MRPLs (minimum required performance limits) proposed by WADA (World Anti-Doping Agency) and reference laboratories of the European Community.