Kinetic equation with exact charge conservation

A kinetic master equation for multiplicity distributions is formulated for charged particles which are created or destroyed only in pairs due to the c onservation of their Abelian charge. It allows one to study time evolution of the multiplicity distributions in a relativistic many-body system with a rbitrary average particle multiplicities. It is shown to reproduce the equi librium results for both canonical (rare particles) and grand canonical (ab undant particles) systems. For canonical systems, the equilibrium multiplic ity is much lower and the relaxation time is much shorter than the naive ex trapolation from grand canonical results. Implications for chemical equilib ration in heavy-ion collisions are also discussed.