The slow motion of two rigid spherical particles along the line through their centers in an unbounded viscous fluid is considered, The fluid is allowed to slip at the surfaces of the particles, Also, the particles may differ in radius, in slip coefficient, and in migration velocity (or in applied force), Using spherical bipolar coordinates, the creeping flow equations are solved in the quasisteady situation, and the interaction effects between the particles are evaluated for various cases, The interaction between particles is found to be more significant when the slip coefficients at the particle surfaces become smaller. In general, the influence of the interaction on the smaller particle is stronger than on the larger one, The creeping motion of a spherical particle in the direction perpendicular to a plane wall is also studied for the case in which the solid-fluid interfaces may have different slip coefficients. The retarding effect of the plane wall on the motion of the particle can be very significant when the surface-to-surface distance gets close to zero. Our results for the particle-particle and particle wall interaction parameters at any separation distance agree very well with the existing solutions for the limiting situations of no slip and perfect slip at the solid-fluid interfaces.