This study evaluated the capability of the Abbott TDx assay to test for propoxyphene in urine and various biological samples, including tissues obtained from three fatal overdoses, by comparison to gas chromatography/mass spectrometry (GC/MS). First, within-run and between-run precision were determined using three control samples (200, 400, and 900 ng/mL) tested over a two-week period. Within-run coefficients of variation (CV) for the three controls were 1.4, 2.2, and 2.5%, respectively; the between-run CVs were 2.5, 3.1, and 4.0%, respectively. The cross-reactivity with norpropoxyphene, the major metabolite of propoxyphene, was concentration dependent and in the range of 29.3 to 92.6%. Propoxyphene and its metabolite were assayed in biological samples the same day using the Abbott TDx and GC/MS. Tissue preparations were analyzed by TDx without specimen pretreatment other than homogenization and dilution with saline. The TDx results were in accordance with the results obtained by GC/MS.