We investigated the adsorption of Li on the Si(100) surfaces of n- and p-type doped samples. ΔΦand TDS measurements show the well known features for adsorption on the n-type sample, but unusual behaviour on the p-type one. A closer inspection clearly indicates strong bulk diffusion into the p-type sample. The dependence of the diffusion rate on the doping can be retraced to the solubility of Li in silicon which strongly depends on the acceptor concentration.