The purpose of this study was to compare the pharmacokinetic profiles at steady-state of the test product, Tramadol HCl Once-A-Day (OAD) 200 mg tablets and the reference product, Tramadol HCl 50 mg (IR) tablets (Ortho-McNeil Ultram®). For this purpose, the extent of absorption of tramadol and formation of O-desmethyltramadol (measures of systemic exposure) after multiple administration of 50 mg 6-hourly at 07:30, 13:30, 19:30 and 01:30 (reference product) and 200 mg 24-hourly at 07:30 (test product), were compared.