A continuous dissolution/absorption system using a hexadecane membrane (HDM) as the permeation measurement has been examined for three distinct formulations of metformin hydrochloride. This system was used to correlate the absorption rate of metformin through the membrane after release from the dosage form to rate of appearance of metformin in the plasma from the same formulations. These correlations were then used to make predictions of the in vivo plasma profile for each formulation. Successful predictions of AUC were accomplished for both immediate release and extended release formulations of metformin hydrochloride.