Ion beam sputtered Fe/Co multilayers were studied by means of magnetostriction measurements and conversion electron Mössbauer spectroscopy. With decreasing period of modulation the magnetostriction constant of the total multilayer increases. This effect can be attributed to the presence of Fe-Co interdiffusion layers having a large positive magnetostriction. Assuming a linear concentration gradient between the individual Fe and Co layers an interdiffusion layer thickness of about 10 Å can be calculated from the magnetostriction data. The Mössbauer spectra of the Fe/Co multilayers showed an increasing asymmetrical broadening with decreasing modulation wavelength. An atomic layer model was applied to explain the observed spectra again assuming a linear concentration gradient. A good fit can be obtained assuming an interdiffusion layer consisting of 5-6 atomic planes, i.e. having a thickness of 10-12 Å. Both techniques proved to be good tools for studying interface effects in Fe/Co multilayers quantitatively.