Using synchrotron radiation at the Frascati storage ring ADONE, the X-ray Absorption Near Edge Structure (XANES) has been applied to determine homologies and modifications of the local structure of the calcium binding sites of troponin C. In all four calcium binding sites, Ca2+ appears to be co-ordinated to carboxyl and carbonyl groups in a characteristic configuration. No structural difference has been found between high and low-affinity sites. A distortion of the Ca2+ site geometry by binding of Mg2+ has been observed. The XANES of parvalbumin has been measured and found to be different from troponin C. A tentative identification of the characteristic XANES spectra of the two different Ca2+ sites in this protein is reported.