The objective was to estimate the detection times and metabolite/parent compound ratios in urine after a single dose of buprenorphine. Eighteen healthy volunteers received a single dose of 0.4 mg buprenorphine sublingually. Urine samples were collected prior to dosing and at 2, 4, 6, 8 12, 24, 48, 72, and 96 h post-dose. The samples were screened using cloned enzyme donor immunoassay (CEDIA) reagent and quantitation was performed with liquid chromatography-tandem mass spectrometry (LC-MS-MS) with a cut-off of 0.5 ng/mL for buprenorphine and norbuprenorphine. The mean time of continuous positive results was 9 h (range 4 to 24 h) with CEDIA, whereas for an LC-MS-MS method it was 76 h (range 23-96 h) for buprenorphine, and for norbuprenorphine all samples were positive at 96 h. Some subjects had positive CEDIA results after a negative sample, owing to differences in creatinine concentration. The time when the ratio norbuprenorphine/buprenorphine exceeded 1 was estimated at 7 h. The metabolite/parent ratio may be used to estimate the time of intake even though the individual ratios showed an increased variation the more distant the collection time. We believe that using this ratio, rather than the actual concentrations, it is possible to compensate for urine dilution and different doses, and to improve interpretation.