Ribozymes are RNA or modified RNA polymers capable of catalyzing cleavage reactions in target strands RNA, and are under development as human therapeutics. Previous methods used for quantitation of nucleic acid polymers in serum or plasma required extraction of the polymer followed by capillary electrophoresis, HPLC, or gel electrophoresis. These methods are time consuming and lack sensitivity. A bioanalytical method has been developed that does not require extraction of the ribozyme analyte from serum. This technique relies on hybridization of the ribozyme molecule to two complementary biotin and digoxigenin labeled oligonucleotide probes. Serum containing the ribozyme is mixed with the labeled probes, and the mixture is heated at 75 degrees C for 5 min to disrupt the ribozyme secondary structure. Samples are then cooled to permit probe annealing and are added to a streptavidin-coated 96-well plate. The bound complex is detected with an anti-digoxigenin alkaline phosphatase (AP) conjugate using PNPP (p-nitrophenyl phosphate) as a substrate. The amount of colored product is measured on a microtiter plate reader at a wavelength of 405 nm. Concentrations of unknown ribozyme samples are estimated based on a standard curve (0.37-270 ng/ml) prepared in serum. The validated lower and upper limits of quantification are 5.0 and 120 ng/ml, respectively. The assay can be completed in approximately 5h and does not require extraction procedures or electrophoretic/chromatographic separation. It is therefore a simple, sensitive and rapid technique. This assay has been validated and has been used for quantitation of serum levels of the HEPTAZYME ribozyme in mouse, monkey, and human pharmacokinetic studies.