Using a sample of 3.1 fb(-1) integrated luminosity accumulated with th
e CLEO II detector at the Cornell Electron Storage Ring; we measure th
e ratio of branching fractions B(D-0 --> K- pi(+)pi(0))/B(D-0 --> K(-)
pi(+)) = 3.81 +/- 0.07 +/- 0.26, the most precise determination of thi
s quantity to date.