The kinetics of isothermal crystallization of disperse liquids containing nucleation-active seeds are analyzed in the case of each droplet of the ensemble giving birth to one nucleus only. Expressions are derived for the time dependences of the number of crystallized droplets and the fraction of crystallized volume of the ensemble. The time t1/2 for half-crystallization and the critical supercooling DELTAT(c) of the disperse liquid are determined as functions of the average seed number a (or, equivalently, the volume) of the droplets. It is found that as long as a > 5, the crystallization behavior of the disperse liquid is described adequately by that of the "average" droplet containing a seeds. When a decreases below 5, the crystallization behavior of the disperse liquid departs appreciably from that of the "average" droplet, and when a approaches In 2, t1/2 and DELTAT(c) increase dramatically. This conforms with experiment and implies that by diminishing the seed concentration and/or the droplet volume, the disperse liquid can be prevented from crystallization up to that low temperature at which homogeneous nucleation begins. The results obtained are applicable also to devitrification and polymorphic transformation of disperse solid phases.