The condition for the validity of the orbital motion limited (OML) theory is reviewed, with reference to the calculation of the floating potential attained by a spherical body immersed in a plasma. It is shown that the OML theory is never satisfied in Maxwellian plasmas, even in the case of very small bodies, i.e. those with radii much smaller than the plasma Debye length. The case considered is that where the ion temperature is less than or equal to the electron temperature. The results are relevant to the theory of dusty plasmas, where the OML theory has been much employed.