Loss processes of metastable nitrogen molecules A(3) Sigma(u)(+) in a Townsend discharge have been investigated in N-2/NO, N-2/CCl2F2 and N-2/CH2FCF3 mixtures. The collisional quenching rate coefficients of N-2(A(3) Sigma(u)(+)) by NO, CCl2F2 and CH2FCF3 are determined using a new theory which takes the reflection at the boundary into account in solving the diffusion equation. The collisional quenching rate coefficients of N-2(A(3) Sigma(u)(+)) by NO, CCl2F2 and CH2FCF3 are 4.75 x 10(-11), 8.32 x 10(-13) and 2.96 x 10(-15) cm(3)s(-1), respectively.