The role of condensation in influencing the source term in the cover-gas region of a liquid-metal fast breeder reactor was analyzed. A computer program was developed that considers both coagulation and condensation to solve the integro-differential equation governing the aerosol behavior in the cover-gas region. Our results for a representative case show that condensation can have a very substantial effect on the particle size distribution in the cover gas and hence on the source term in the containment aerosol behavior computer programs.