An approximate method is developed by the aid of which one can determine the perturbative action of one asteroid upon his distance to the other one, durigh the regular proximity of these celestial bodies. The final effect appears to be not sensible during a time interval of "dynamical proximity" inferior to one day, if the mass of the perturbin asteroid is of the order of $10^{-13}$ Sun's mass and the proximity distance is of the order of 0.000005 a.u.