The autoradiographic method has been used for investigation of the local distribution of water diffused into composites consisted of epoxide matrix and carbon fibres. The autoradiographs have shown the inhomogeneity of the concentration of water diffused in the composites. The Joyce-Loebl Mark III microdensitometer served for the quantitative evaluation of the autoradiographs. Autoradiographs made from plastic standards containing tritium have been employed for calibration of the optical density scale of densitometric curves. From the results it can be seen local concentration of the diffused water. The results of autoradiographic measurements have also been correlated to those of ultrasonic ones. From the results it follows that the composite probes with incorrect lamination absorb more water than those with perfect lamination.