The aim of the present study is to perform invitro - invivo correlation for the formulation containing paracetamol and tramadol.To conduct invitro - invivo correlation a validated bioanalytical HPLC method is required.Therefore a HPLC method is to be develop and validated in plasma.Inoder to conduct invitro - invivo correlation formulation with 3 different release rates are required.These formulations will be subjected to invitro dissolution rate and invivo bioavailability.