An electrochemical technique using the assessment of the rate of oxygen reduction at a rotating disk electrode has been used in conjunction with surface analysis by X-ray photoelectron spectroscopy to study the first layer formation of calcareous deposits under cathodic protection in various solutions. The study has shown that the electrochemical technique is an effective means of monitoring scale formation and that the existing models which predict scale formation by a basal layer of Mg(OH)(2) followed by CaCO3 are over-simplified. The advantages of using an integrated approach of electrochemical analysis and a surface sensitive analysis technique in characterising the initial scale as a function of the solution composition are presented and discussed and revised models describing the temporal development of calcareous layers in saline solutions are suggested. (C) 2002 Elsevier Science B.V. All rights reserved.