Abstract We investigate the ABC effect in the reaction n+p → d+( ππ) 0 using the chiral lagrangian of Weinberg in the tree approximation. Chiral-bag-model form factors are used for the vertices. We obtain cross sections as a function of energy for deuteron scattering angles θ d = 0° and 10.5°. The results are compared with the latest experimental measurements. The fit to the absolute value of the cross section is obtained taking the bag radius R as a free parameter; the fitted value of R turns out to be that expected in the light of previous studies in the framework of chiral bag models. The ABC effect is almost completely accounted for in terms of the lowest-order diagrams.