We　report　on　a　protocol　for　a　simultaneous　competitive　immunoassay　for　tetracycline　(TC)　and　chloramphenicol　(CAP)　on　the　same　sensing　interface.　Conjugates　of　TC　and　of　CAP　with　bovine　serum　albumin　were　first　co-immobilized　on　a　glassy　carbon　electrode　modified　with　gold　nanoparticles.　In　parallel,　monoclonal　anti-TC　and　anti-CAP　antibodies　were　conjugated　onto　CdS　and　PbS　nanoclusters,　respectively.　In　a　typical　assay,　the　immobilized　haptens　and　the　added　target　analytes　competed　for　binding　to　the　corresponding　antibodies　on　the　nanoclusters.　Subsequently,　Cd(II)　and　Pb(II)　ions　are　released　from　the　surface　of　the　corresponding　nanoclusters　by　treatment　with　acid　and　then　were　detected　by　square　wave　anodic　stripping　voltammetry.　The　currents　at　the　peak　potentials　for　Cd(II)　and　Pb(II)　were　used　as　the　sensor　signal　for　TC　and　CAP,　respectively.　This　multiplex　immunoassay　enables　the　simultaneous　determination　of　TC　and　CAP　in　a　single　run　with　dynamic　ranges　from　0.01　to　50　ng　mL-1　for　both　analytes.　The　detection　limits　for　TC　and　for　CAP　are　7.5　pg　mL-1　and　5.4　pg　mL-1,　respectively.　No　obvious　nonspecific　adsorption　and　cross-reactivity　was　observed　in　a　series　of　analyses.　Intra-assay　and　inter-assay　coefficients　of　variation　were　less　than　10　%.　The　method　was　evaluated　by　analyzing　TC　and　CAP　in　spiked　samples　of　milk　and　honey.　The　recoveries　range　from　88　%　to　107　%　for　TC,　and　from　91　%　to　119　%　for　CAP.　[Figure　not　available:　see　fulltext.]　©　2013　Springer-Verlag　Wien.