Recently a new kind of computational technique for kinetic plasma simulation has been developed, making use of particles of variable shape (blobs). The aim of the present work is to derive a kinetic equation governing the evolution of the blobs and solve it in the case of small perturbations. Results are compared with those obtained for the real plasma and for a plasma of particles of fixed shape (the model usually employed in popular particle-in-cell simulations). The comparison is useful to find out whether the additional cost of dealing with more degrees of freedom is balanced by the superior accuracy provided by the new technique in describing the phase-space distribution. (C) 1996 American Institute of Physics.