The long-term evolution of accreting carbon-oxygen white dwarfs in close binary sistems is considered. The mass of the star is M = 1.3 MO and the rate of accretion M = 10-10 MO yr-1. The effects of solidification of the star's interior are studied by considering three different cases of chemical separation, associated with different cooling times. The results show that diverse outcomes are possible, ranging from total collapse for maximum separation to off-center ignition for partial chemical differentiation
