This study sought to develop a method of improving the differential diagnostic between healthy and obstructed kidneys using only parameters derived from the 99mTc-MAG3 renogram. The analysis included data from 46 healthy and 36 obstructed kidney units. The parameters calculated were: mean transit time (MTT), time at 20% of the initial height of the renal retention function (T20) and time to peak of the renogram (TP). A discriminant analysis was carried out to obtain a discriminant function in order to differentiate between the two groups. The best results were obtained using the function: (2.5629 InT20) + (2.1280 In TP) -27.1224 which correctly classified 97.56% of the cases, giving a sensitivity of 94.44% and a specificity of 99.99%.