The effect of retardation in the van der Waals interaction between two spherical particles is examined theoretically. The expressions which can be applied to Ka⩽ ⩽ obtained, in whichKis Debye-Hukel parameter, a is the radius of particles, D is the shortest distance between two spheres. An extensive comparison of exact, sophisticated and simplified treatments has been described. Computation results show that the improved approximations agree fairly well with exact computations and can be considered as the supplement of the classical Hamaker results. They should find application in problems of colloid stability and particle deposition.