An improved telomerase assay was developed that allows direct quantification of the enzyme activity by scintillation counting of the labeled telomerase product. The assay measures the incorporation of 32P-dGTP into telomeric repeats synthesized at the 3' end of a biotinylated primer. Telomerase reaction product is separated from the reaction mix by streptavidin-coated magnetic beads and counted. The assay can be used for quantitative studies of human telomerase and its inhibitors.