That silicon could become an important tissue-compatible biomaterial is suggested by recent results. First observations are reported here of the significant effects that electrical bias has on the calcification process under simulated acellular physiological conditions. Cathodic current flow through porous silicon is shown to accelerate the kinetics of calcium phosphate deposition. Reasons why formation is restricted to the cathodically biased region and why calcium phosphate is not formed within the silicon layer are discussed.