Heterogeneous immunoassays using CdSe/ZnS quantum dots (QDs) to label anti-progesterone antibody (P4Ab) were developed for the determination of progesterone (P4) in the wells of a 96-well microtiter plate. P4Ab was conjugated to hydrophilic CdSe/ZnS QDs via ethyl-3-(dimethylaminopropyl) carbodiimide (EDC)-N-hydroxysuccinimide (NHS) chemistry (QDs-P4Ab conjugates). The QDs-P4Ab conjugates were employed as a second antibody in a sandwich immunoassay or immobilized onto the 3-aminopropyltrimethoxysilane (APTMS) sol-gel membrane in a direct binding assay. The sandwich immunoassay had a detection limit of 553.9 pg/ml and a sensitivity of 18,251.96 pg/ml with a linear range of 2,184.6 ? 117,082 pg/ml, while the direct binding immunoassay had a linear range of 28.95 ? 26,607.7 pg/ml with a detection limit of 3.32 pg/ml and a sensitivity of 987.24 pg/ml. These fluorescence immunoassays have been successfully applied for the determination of P4 in real human serum, and the results were well correlated with those of a certified radioimmunoassay (RIA) method.