A derivation of sectional equations for mass exchange between colliding droplets during head-on collisions of multisize (polydisperse) sprays is presented. The collision terms of these equations account for binary collisions which lead to coalescence and immediate break-up into two new droplets which differ in mass from the original droplets. That is, mass is exchanged between the original droplets. The amount of exchanged mass is allowed to vary between 0 and 100% of the mass of the donor droplet. The new equations are employed here to analyze the time evolution in droplet size distributions of two head-on colliding polydisperse sprays.