Water sorption and solubility of six proprietary composite resin materials were assessed, and monomers eluted from the organic matrix during water storage identified. Water sorption and solubility tests were carried out with the following storage times: 4 h, 24 h and 7, 60 and 180 days. After storage, water sorption and solubility were determined. Eluted monomers were analysed by high performance liquid chromatography (HPLC). Correlation between the retention time of the registered peak and the reference peak was observed, and UV-spectra confirmed the identity. The results showed an increase in water sorption until equilibrium for all materials with one exception. The solubility behaviour of the composite resin materials tested revealed variations, with both mass decrease and increase. The resin composition influences the water sorption and solubility behaviour of composite resin materials. The HPLC analysis of eluted components revealed that triethyleneglycol dimethacrylate (TEGDMA) was the main monomer released. Maximal monomer concentration in the eluate was observed after 7 days. During the test period, quantifiable quantities of urethanedimethacrylate (UEDMA) monomer were observed, whereas 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane (Bis-GMA) was only found in detectable quantities. No detectable quantities of bisphenol-A were observed during the test period.