A new fluorescent technology called homogeneous time-resolved fluorescence (HTRF) is sensitive, homogeneous, and quite tolerant to extremes in reaction conditions. These characteristics make this technique an attractive candidate for use in high throughput screens. The assay system uses a pair of fluorescent compounds to label biomolecules. The long-lived nature of the fluorescence of one of them, europium cryptate, facilitates the homogeneous nature of the assay. Furthermore, the introduction of a time delay in reading the signal eliminates the principal difficulty in applying fluorescence to screening formats, that of endogenous fluorescence of samples tested (especially natural products). This technique is robust and sensitive, and we report here its utility in a high throughput screening format.