Quantum dots (QDs) have the potential to simplify the performance of multiplexed analysis. In this work, we prepared bioinorganic conjugates made with highly luminescent semiconductor nanocrystals (CdSe-ZnS core-shell QDs) and antibodies to perform multiplexed fluoroimmunoassays. Sandwich immunoassays for the detection of cholera toxin, ricin, shiga-like toxin 1, and staphylococcal enterotoxin B were performed simultaneously in single wells of a microtiter plate. Initially the assay performance for the detection of each toxin was examined. We then demonstrated the simultaneous detection of the four toxins from a single sample probed with a mixture of all four QD-antibody reagents. Using a simple linear equation-based algorithm, it was possible to deconvolute the signal from mixed toxin samples, which allowed quantitation of all four toxins simultaneously.